You are right: Sometimes we sin without even realizing it - and not just by doing something wrong, but by failing to do something right. We may ignore someone who needs our help or encouragement, for example, or we may fail to pray for them or in some other way overlook their need.
Is God displeased even when we don't realize we have sinned? Yes - because all sin is wrong in His eyes, and even if we don't acknowledge it as sin, God sees it and knows what we have done. The Bible says, "Nothing in all creation is hidden from God's sight. Everything is uncovered and laid bare before the eyes of him to whom we must give account" (Hebrews 4:13).
I want you to understand, however, why God is displeased when we sin. First, God knows that whenever we sin, we are hurting ourselves (as well as others). But God loves us, and He hates what sin does to us. He hates sin so much that He sent His only Son into the world to take away our sins by His death on the cross. Have you turned to Christ for the forgiveness you need?
But God also is displeased when we sin (whether or not we realize what we've done), because it means we have turned our backs on Him and aren't sensitive to Him and His will. Don't let this be true of you. Instead, let your prayer be that of the psalmist: "Create in me a pure heart, O God, and renew a steadfast spirit within me" (Psalm 51:10).