I once heard from Tzvi Freeman this vort. He brought down, in the name of the Baal Shem Tov, and said that we should spread out this teaching far and wide.
The Baal Shem Tov said, it is not the bite of the snake that kills, but the venom that follows.
In spiritual speak this means that it is not the sin that kills the man, but the thoughts that follow that do him in.He sinned, fine. So now pick yourself up and go on, start anew; persevere. But here comes the poison and starts filling our minds with guilt, how could I? It's such a terrible thing that I did! I am so low, so sick, so terrible. These thoughts can literally kill a person. In our times we cannot be involved with any negative thoughts at all. In fact, a person might think that since he has felt guilty then that is enough of an atonement for the wrong he has done, in front of G-d or man. The only way to undo a wrong is to change our behaviour, not by thinking of the sin.
So remember, it's not the bite that kills, it's the venom that follows.