People can't be good enough.

God built the universe with perfection. Not one law of the universe fails. This is why you can do scientific experiments over and over. If you do them exactly the same, they produce exactly the same results.

The mistake that can't be perfected by mankind is love for God. It is the foundational, core law of the universe. The second is love for mankind. Even though one might be able to come back from making these core mistakes so that he doesn't make them anymore, once it is done, it is don. Time cannot be altered, at least not by anything that we have the ability to do.

Only God has the power to make the correction. He did it in Jesus God, who took the punishment that we would receive as a natural result of our mistake-making.

Since the foundational law of the universe is mankind's love for God, we need to understand that God exists so that we can attempt to love Him. Denying Him is denying our only source of salvation, since we can't save ourselves.