Read the "Flood"
"... every inclination of the thoughts of the human heart was only evil all the time."Imagine a world where every human thought was evil, only evil, not even a little good, all the time. Today evil exists, people have evil thoughts and do evil things, we all have evil thoughts, even "good" people, but not to the extent of every thought, only evil, all the time. The World of Noah was a terrible place. Life was full of fear, terror and evil. Imagine a world like that.
"... his heart was deeply troubled."Or as rendered in a different translation of the bible "it broke His heart." The Creator's heart was filled with pain at all the horrible thoughts and actions of the people he had created. In his mercy, he ended the suffering in this evil-polluted world with the swift judgment of the Flood.