Adam not only ate the fruit that Eve gave to him but he had heard what the serpent implied about God. The serpent presented a twisted motive concerning the tree of Knowledge and Adam said nothing to correct it. Then he passed the buck to Eve when Jesus questioned him. Eve then passed the buck on to the serpent when given the opportunity to admit her action. There is no evidence that they asked forgiveness for what they had done even after God dealt out His punishments.
Cain, rather than accepting the rebuke and offer of resubmitting his offering with the proper attitude he compounded his sin rather than listen to Jesus and doing what was offered to correct his sin. Jesus asks Cain what has happened, even though He knew, offering Cain the chance to come clean. Instead, what did Cain do? He whined to God about how unfair his punishment was. What a wicked and self-serving people we are. Even then Jesus did not strike Cain down. He had mercy and protected Cain from vengeance.
God has so much patience with us. It is astounding to me. I need to remember this and extend that same patience to others. I need to admit my sin to God and truly regret and repent of it. I need to listen when the Spirit questions me on my actions so that I can recognize when I sin and own up to it, not pass the buck or rationalize it away. I need to accept the consequences and do right to be accepted by God instead of whining as to how unfair life is treating me or rationalizing away my sin. By doing this I can learn to be the person who walks with God and hopefully draw others to Him.