It is all about attitude. If you willfully sin knowing it is against God, it is counted against you until you repent.
1 John 5:17
English Standard Version (ESV)
17 "All wrongdoing is sin..."
A Sin of Omission is failure to do what one can and must do.
A Sin of Commission is to know something is against God and do it anyway.
There are sins of ignorance...sinning and do not realize that it is a sin.
I believe the Bible gives the best answer; at least this is what helps me understand the subject, maybe it will help others:
James 4:17
Therefore to him that knows to do good, and does it not, to him it is sin.