"Hesitation leads to defeat"

No.

Obviously, the opposite, use of judgement, could be wise.

From where did you pick your bon mot?

Something like, "He who hesitates is lost"

Said opposite of "Look before you leap," but not quite

That's the thing about aphorisms--you can find one to support you no matter what you want to do. And you can find one to support exactly the opposite position too. This one is like the Latin "Carpe diem" except it's 2000 years later.