God knows us better than we know ourselves! He sees us exactly how we are, but we can be deceived and think things like:
we have no sin
we don't need to confess anything
we won't be forgiven when we confess
So it is good to regularly ask God to search us and show us how we are really doing - and then to deal with it!
Psalm 139, 1 Timothy 4:2, 1 John 1:7-10, Romans 8:1-2