unless one ...; if one does not ...
if (it) doesn't exist; if there is no ...; if (one) doesn't have ...
勇気がなけりゃ無理だ。
Without courage, it's impossible.
目標がなけりゃやる気が出ない。
Without a goal, you can't get motivated.
準備をしっかりしておかなけりゃ後悔するよ。
If you don't prepare properly, you'll regret it.