Christians believe that when Adam and Eve sinned in Eden and turned away from God they brought sin into the world and turned the whole human race away from God.
From the Islamic perspective, happiness is a lifelong process aiming for eternal happiness, peace of mind, tranquility of heart, contentment in this world and everlasting bliss in the Hereafter.
If God is all-powerful, then God can prevent all evil. If God is perfectly good, then God should prevent all evil. And yet, evil exists. How can this be true?