From Pliny the Younger’s Epistles (7.26):
Possum ergo quod plurimis verbis plurimis etiam voluminibus philosophi docere conantur, ipse breviter tibi mihique praecipere, ut tales esse sani perseveremus, quales nos futuros profitemur infirmi. Vale.
So here for our guidance is the rule, put shortly, which the philosophers seek to express in endless words and volumes: in health we should continue to be the men we vowed to become when sickness prompted our words.
I found this cited in Robert Burton’s Anatomy of Melancholy (Part. 1 Sect. 1 Memb. 1 Subs. 1) but his imprecision of quotation drives me mad if I don’t have the OET commentary volumes at hand. The above becomes:
summum esse totius philosophiae, ut tales esse sani perseveremus, quales nos futuros profitemur infirmi
This is the sum of all philosophy – in health we should continue to be the men we vowed to become when sickness prompted our words
Which when googled for the source only ends up putting you into a loop always connecting back to Burton.
Extracts 