Literal translation:

He who has kept himself well hidden has lived well.

The perfect tense ("has lived") is important because the meaning is that

"a good life is a quiet life"

- i.e. living in obscurity / not seeking fame - and you cannot say about someone that her/his life is really a good life until s/he "has finished living" (vixit).

As has already been said, it's a quotation from Ovid's Tristitia.