Genesis 6:5 And GOD saw that the wickedness of man was great in the earth, and that every imagination of the thoughts of his heart was only evil continually.
Man always wants to do his own thing. All of mankind imagines themselves as making their own decisions, indirectly being their own god. They would never admit that but man, the public, people want to decide what is right and wrong. They are not willing to believe the Bible or what God has to say.
God looked at man. He saw that man was and will always be a failure. Man will always do wrong. Man is a sinner. He may think that he is doing good but it will be based on public opinion or his own opinion but not what God says!
Humans, naturally, do not want to know what God says. They do not want to live up to a standard that they didn’t set. Their thoughts are of themselves. What they think and what they feel are their greatest motivations.
Man wants to decide what is right! That way he can feel good about it and himself.
Their thinking evil continually doesn’t mean that they always do horrible things. It means that God is far from their thoughts. It means that they have rebelled against their creator God. It means that they want to do whatever they want and certainly not what God wants.