Why do we do things which we know that we'll regret later?

Innately, we know what we do is harmful, and that it'll hurt, but somehow, we cant resist the temptation, and after the deed is done, it feels like someone just stabbed you in the heart.
You are then left bleed and to ponder upon your actions and everything that happened.

Have a little faith, he said. Well i will. Only because i think its worth it.