"... cuanto más agudo entendimiento tienen los jóvenes, más inclinados están a confundirse en sus negocios, pues saben cómo comenzarlos, pero no saben cómo los han de terminar, y así se equivocan con gran daño para ellos, si no hay quien los guíe."

And one translation:

"It is well known that, although the young may not be deficient in understanding and spirit, yet they may commit many errors : having a mind to see the right thing to be done, but, wanting perseverance and a good guide, never complete anything."

another translation

... the sharper the understanding young men have, the more inclined they are to fail in their business dealings, because they know well how to start, but they don't know how to manage them, and so, they self inflict a great harm, if they lack a mentor.  

References

https://www.cervantesvirtual.com/obra-visor/el-conde-lucanor--0/html/00052e2a-82b2-11df-acc7-002185ce6064_1.html

https://archive.org/details/CountLucanorYork1889/page/n175/mode/2up

 

The Russian historian, Mikhail N. Pokrovsky (1868-1932) said that:

History is politics projected into the past

What's pleasing in prose?

Good advise for writing

"nothing can permanently please, which does not contain in itself the reason why it is so, and not otherwise."

Samuel Taylor Coleridge, Biographia Literaria (1817)

What use is liberty?

Marcus Duronius, tribune of the plebs, said (cited by Valerius Maximums)  

... quid opus libertate, si volentibus luxu perire non licet?

• "For what signifies liberty, if we are not permitted to ruin ourselves by luxury if we think fit?" Rollin
• "what use is liberty if we are not allowed to go to perdition with luxury as we want to?" Shackleton-Bailey

And this got him expelled from the senate by the censors  M. Antonius (65) and L. Valerius Flaccus (97 BC). 

Qui observat ventum non seminat

Risk 

Qui observat ventum non seminat; et qui considerat nubes numquam metet. Ecl 11:4

Rashi says:

And he who looks to the clouds. He observes the clouds, and when he sees them darkening, he is afraid to harvest on account of the rains; he will never harvest because he is always fearful [of the rains].

 

Utility Theory and wealth management:

mane semina sementem tuam et vespere ne cesset manus tua quia nescis quid magis oriatur hoc an illud et si utrumque simul melius erit. Ecl. 11:6

 

Unconquerable laws of necessity

Sed invictae leges necessitudinis pectus alioquin procul amentia remotum prodigia ista iusta aestimatione perpendere passae non sunt. Libri novem factorum Dictorumque memorablium, v.1

But the unconquerable laws of necessity did not suffer Pompey's mind, otherwise far removed from folly, to weigh these prodigies in just assessment.

Ex verbis sensum sequamur

Ex verbis sensum sequamur, et ex sensu rationem intelligamus, et ex ratione veritatem apprehendamus. 

In Matthias Flacius, Catalogus de Testium Veritatis, iv, 151 

(Hilarius Pictaviensis, De Trinit. Lib. 5)

From the words let us follow the sense, and from the sense discern the reasons, and from the reasons learn the truth. (my translation).

Objectives always in sight

"Keep your important objectives always up, paramount in sight."

Philosophers...unmanly, avoiding the business of the city and marketplace

Aulus Gellius addressed the role of philosophy in life.

"Philosophy, Socrates, is indeed a nice thing, if one pursue it in youth with moderation; but if one occupy oneself with it longer than is proper, it is a corrupter of men. For even if a man be well endowed by nature and follow philosophy when past his youth, he must necessarily be ignorant of all those things in which a man ought to be versed if he is to be honourable, good and of high repute. For such men are ignorant both of the laws relating to the city, and of the language which it is necessary to use in the intercourse of human society, both privately and publicly, and of the pleasures and desires of human life; in brief, they are wholly unacquainted with manners. Accordingly, when they engage in any private or public business, they become a laughing-stock; just exactly as statesmen, I suppose, become ridiculous when they enter into your debates and discussions ... to be a philosopher is not dishonourable when one is young; but when one who is already older persists in the business, the thing becomes laughable, Socrates, and I for my part feel the same towards those who philosophize as towards those who lisp and play. Whenever I see a little boy, to whom it is fitting to speak thus, lisping and playing, I am pleased, and it seems to me becoming and liberal and suited to the age of childhood; but when I hear a small boy speaking with precision, it seems to me to be a disagreeable thing; it wounds my ears and appears to be something befitting a slave. When, however, one hears a man lisping, or sees him playing, it appears ridiculous, unmanly and deserving of stripes. I feel just the same way towards the philosophers When I see philosophy in a young man, I rejoice; it seems to me fitting, and I think that the young man in question is ingenuous; that he who does not study philosophy is not ingenuous and will never himself be worthy of anything noble or generous. But when I see an older man still philosophizing and not giving it up, such a man, Socrates, seems to me to deserve stripes. For, as I have just said, it is possible for such a man, even though naturally well endowed, to become unmanly, avoiding the business of the city and the marketplace, where, as the poet says, men become “most eminent,” and living the rest of his life in hiding with young men, whispering in a corner with three or four of them, but never accomplishing anything liberal, great or satisfactory...He does not, of course, refer to that philosophy which is the teacher of all the virtues, which excels in the discharge of public and private duties alike, and which, if nothing prevents, governs cities and the State with firmness, courage and wisdom; but rather to that futile and childish attention to trifles which contributes nothing to the conduct and guidance of life, but in which people of that kind grow old in “ill-timed playmaking,”

Robert Burton in "Anatomy of Melancholy" also touches on the issue, and is

Your greatest students are commonly no better, silly, soft fellows in their outward behaviour, absurd, ridiculous to others, and no whit experienced in worldly business; they can measure the heavens, range over the world, teach others wisdom, and yet in bargains and contracts they are circumvented by every base tradesman. Are not these men fools? and how should they be otherwise, but as so many sots in schools, when (as he well observed) they neither hear nor see such things as are commonly practised abroad? how should they get experience, by what means? "I knew in my time many scholars," saith Æneas Sylvius (in an epistle of his to Gasper Scitick, chancellor to the emperor), , "excellent well learned, but so rude, so silly, that they had no common civility, nor knew how to manage their domestic or public affairs." 

Marcus Aurelius Meditations

Concentrate every minute like a Roman—like a man—on doing what’s in front of you with precise and genuine seriousness, carefully, willingly, with justice. And on freeing yourself from all other distractions. Yes, you can—if you do everything as if it were the last thing you were doing in your life, and stop being aimless, stop letting your emotions override what your mind tells you, stop being hypocritical, self-centered, irritable.

Do external things distract you? Then make time for yourself to learn something worthwhile; stop letting yourself be pulled in all directions.

People who labor all their lives but have no purpose to direct every thought and impulse toward are wasting their time—even when hard at work. 

Don’t waste the rest of your time here worrying about other people—unless it affects the common good. It will keep you from doing anything useful. You’ll be too preoccupied with what so-and-so is doing, and why, and what they’re saying, and what they’re thinking, and what they’re up to, and all the other things that throw you off and keep you from focusing on your own things. 

If you do a job in a principled way, with diligence, energy and patience, if you keep yourself free of distractions, and keep your thoughts ... then your life will be happy.

Choose not to be harmed—and you won’t feel harmed. Don’t feel harmed—and you haven’t been 

Most of what we say and do is not essential. If you can eliminate it, you’ll have more time, and more tranquility. Ask yourself at every moment, ‘Is this necessary?’

Remember that our efforts are subject to circumstances; you weren’t aiming to do the impossible. Aiming to do what, then? To try. And you succeeded. What you set out to do is accomplished.

Tell yourself: This thought is unnecessary. This one is destructive to the people around you. This wouldn’t be what you really think (to say what you don’t think—the definition of absurdity).

Text taken with some modifications from Gregory Hays' translation of Meditations.

Phrases from reading

Rembrandt: Philosopher in meditation

• Seneca: Genus dicendi mutatur per publicos mores (version of Whiterspoon). Regarding the involution of the spoken English.
• Ponite corda in verba Dt 32:45
• Res et verba Philippus; verba sine re Erasmus; res sine verbis Lutherus: nec res, nec verba Carolostadius; Table Talks DCCCII. 
• parum ordinavit, multa accumulavit referred Burton regarding those who write immethodically.
• Infelix operis summa, quia ponere totum nescit, unhappy that who's skilled in details, but not in the whole work, regrets Horace. BUT read next what Luther said:
• ...da ist kein divisio mehr, sed est punctum mathematicum, ibi (principles cannot fail there).  Et hoc est ... redigere omnia ad primum principium, id est, ad genus generalissimum. WA, Tischreden, (1) #312, p. 128. (Table Talk p. 42).
• Ad spem veterem, to the old hope, in the frontispiece of a roman monument. 
• a minori ad maius, reasoning from minor to major, similar to the qal wahomer.
• deductio ex sensibilibus: deduction from empiricals.
• adaequatio intellectus et rei: adequation of the intellect to things (correspondence). Or to paraphrase Hermann Lotze (Logica #130, p. 156), "thought follows reality". A frequent assumption (and fallacy) in science.
• Et cui assimilastis me, et adaequastis, dicit Sanctus? Is. 40.25
• Ex singularibus ad universalia, Luther table talk on Astronomy and Mathematics. p. 315
• pastione venti et re inutili, Ben Ezra's rendering of Ec. 1:14 quoted in Munsterus Hebraica Biblia Latina, p. 1573
• Cessante causa, cessat effectus. A. Tiraquelli. "effect follows cause with unerring certainty". White
• Ignorantia factis non iuris excusat. Sebastiano Medicis.
• concursio rerum fortuitarum, Cicero
• natura sunt immutabilia quoted in Petrus Santerna
• In obscuris, inspici solere quod, verisimilius est, aut quod plerumque fieri solet. Paulus
• “...eritque similis huic dies crastinus, imo major, excelentior valde... / erit sicut hodie, sic et cras, et multo amplius / eritque similis huius dies crastinus, multo celeberrimus” (Is.56:12 Tremellius/Vulgate/Chastellion)
• Patet hinc, certitudinem harum scientiarum unice dependere a certitudine ipsorummet principiorum, non a modo formandi conclusiones, quae omnes evidentissimo ratiocionio ex principiis deduci debent. Quae ratio est, cur Mathesis abstracta sit invictae certitudinis; Astrologia vana & futilis; Caeterae vero, mediae certitudinis inter utramque: quoniam talia sunt principia, quibus illae superstructuae sunt. Theses Miscl. XII J. Bernoulli, Opera p.233-234. 
• Parvus error in principiis, magnus in conclusionibus. Aristotle, De Caelo i, 5
• Parvus error in principiis, magnus in conclusionibus.
• Parvus error in initio magnus erit in fine. Aquinas
• Parvus error in principiis, maximum facit in conclusionibus. Aristotle acc. Albertus Magnus
• Parvus error in principio, magnus in fine est. Giordano Bruno, De Immenso, Innumerabilis et Infigurabilis II, i
• parvus error in principio intolerabilis sit in fine. Johannis Peckham, 
• Felix qui potuit rerum cognoscere causas, Virgil (Georgics, 2.490). (Happy that who understands the causes of things)