It seems the phrase in question comes right before the talk about establishment of a school. In the Greek, this is that sentence right before the school one:
Quoteκαὶ ἐπιχαρήσεσθαί τινι ἐπὶ τῷ διορθώματι
So, we can try to dissect it and see what we come up with. Here we go...
καὶ = just and conjunction: "and, also, etc"
ἐπιχαρήσεσθαί http://www.perseus.tufts.edu/hopper/morph?l=e%29pixarh%2Fsesqai%2F&la=greek&can=e%29pixarh%2Fsesqai%2F0&prior=kai\&d=Perseus:text:1999.01.0257:book=10:chapter=1&i=1#lexicon
Ah! So, that's where the ambiguity is coming in! The definition LSJ gives is "rejoice over, exult over, mostly of malignant joy" but also "rarely in good sense, to rejoice in another's joy". The first sense is followed by the dative case, the latter by the accusative. The word used here is in the future infinitive middle. The middle "tense" always points back to the individual so I could see this meaning "will take joy in one's own misfortune." Maybe.
τινι "to anyone/anything" (dative)
ἐπὶ τῷ διορθώματι "for a means of correction, or setting right." http://www.perseus.tufts.edu/hopper/morph?l=diorqw%2Fmati&la=greek&can=diorqw%2Fmati0&prior=tw=|&d=Perseus:text:1999.01.0257:book=10:chapter=1&i=1#lexicon
As y'all know, my ancient Greek is rudimentary, but I could see this line meaning that the wise one rejoices in their own misfortunes because they can use it as a means of correction for themselves. If they mess up, it's seen as an opportunity for correction. I would need to see more translations but I think that's at least plausible looking at the Greek.