Judges 16:28
O Lord God, please remember me. Strengthen me, O God, just once more...
A penitent man realizes his folly and knows that he doesn't deserve mercy. He realizes that he had sinned against God and God alone. Samson realized his sin and disobedience when he gave into his nagging wife Delilah. But, towards the end of his life he understood his sin and begged God for His forgiveness. The Bible says that Samson killed more Philistines in his death than when he was alive.
It's never too late to repent. Like the thief on the cross our lives will still amount to something with God's grace, even at the last moment.