Opportunity seldom knocks twice

This page is about the saying "Opportunity seldom knocks twice"

Possible meaning:
Take any opportunity or chance when it comes - it may not come again.

Note:
opportunity (noun) = a lucky chance; a set of circumstances that makes it possible to do something | seldom (adverb) = rarely | knock (verb) = strike or hit (a door) noisily to attract attention | twice (adverb) = two times