There is that interpretation, callis, but my dad mainly used it to encourage people to try to do something they didn't think they'd be any good at. You'll never know till you try and, in any case, if you like, say, playing football then you should play football even if you're not very good at it.
Paraprosdokians are figure of speech where the latter part of the phrase is humorously surprising or unexpected and causes the reader or listener to reframe or reinterpret the first part.