“Often a terrible wind follows hard after fair-sailing.”

ἀντιπνεῖ δὲ πολλάκις εὐτυχίᾳ δεινά τις αὔρα

Hermolochus just defeated Wikipedia. Stobaeus made the cut, though.

(Am I the only one who loves the sound of ἀντιπνεῖ? Seriously, say it aloud a few times…)