Fortune is bald behind

And so must be seized by the forelock. Which is to say... it is easy to see things in retrospect. A proverb I first met in the form in one of Patrick O'Brian's book; I think in the mouth of Captain Aubrey (no! It was the governor).

To my delight, I find it in Carmina Burana:

Verum est, quod legitur, fronte capillata, sed plerumque sequitur Occasio calvata.

It is written in truth, that she [Fortuna] has a fine head of hair, but, when it comes to seizing an opportunity she is bald.