We can all recognize that the world, and the people who live in it, are not perfect. But the world was once perfect, and people had a perfect relationship with God, the creator of the universe.
But one day, the first man and woman, Adam and Eve, decided to disobey God and eat from a tree that they thought would give them knowledge of everything. This was a mistake. When we disobey God, it is called sin. Sin separates us from God.