Erasmus, letter to Christian Northoff (tr. R.A.B. Mynors and D.F.S. Thomson):
And do not be ashamed to ask questions if you are in doubt, or to be put right whenever you are wrong. Avoid working at night and studying at unsuitable times and seasons; these things quench the light of the mind and are very bad for health. Aurora is the Muses' friend: daybreak is an excellent time for study. After lunch, take some recreation, or go for a walk, or enjoy gay conversation; reflect that even such activities as these can afford opportunity for studying. As to food, eat only what suffices for health, and not so much as you long to eat. Take a short walk before supper, and again after it. Just before you go to sleep you should read something of exquisite quality, worth remembering; let sleep overtake you while you are musing upon it and when you awaken try to recall it to mind. Always keep fixed in your heart Pliny's dictum [Letters 3.5.16] that all the time which one fails to devote to study is wasted, and reflect that youth is the most fleeting thing on earth, and that when once it has fled away it never returns.
Ozias Leduc, The Young Student
Nec sciscitari si quid dubitas, nec castigari si quid errabis, sit pudor. Nocturnas lucubrationes atque intempestiva studia fugito; nam et ingenium extinguunt et valetudinem vehementer offendunt. Aurora Musis amica est, apta studiis. Pransus aut lude, aut deambula, aut hilarius confabulare. Quid quod inter ista quoque studiis locus esse potest? Cibi non quantum libidini, sed quantum valetudini satis est sumito. Sub coenam paulisper inambula, coenatus idem facito. Sub somnum exquisiti quippiam ac dignum memoria legito, de eo cogitantem sopor opprimat, id experrectus a teipso reposcas. Plinianum illud semper animo insideat tuo, omne perire tempus quod studio non impertias. Cogita iuventa nihil esse fugacius, quae ubi semel avolarit, redit nunquam.