If you don’t mourn over your sin, you may be complacent toward it.
It’s such a good thing to mourn over your own sin, because then you are sincerely sorrowful over your disobedience to God! That is a good thing. If you didn’t feel bad for going against the ways of the Lord, then you would feel bad only that you got caught—not that you did wrong. Have a heart that is in tune with God’s truth; a heart that repents quickly!