Flint pebble

Fallen man is not simply an imperfect creature who needs improvement: he is a rebel who must lay down his arms. Laying down your arms, surrendering, saying you are sorry, realizing that you have been on the wrong track and getting ready to start life over again from the ground floor – that is the only way out of a hole. This process of surrender, this movement full speed astern, is what Christians call repentance.

Source: Mere Christianity