Satan influenced it, man fell for it, man carries on with it. Satan is pleased with it. So evil originally came from Satan, through his evil influences, man fell for Satan's lie. Man blames God. God sends Jesus to die, to pay for our sins, But sat still influences evil, through men, mam is weak, when i mean man, i mean man/woman we are weak, we are only strong when we are in standing next to God.
Satan however is not to blame all the time, But you can blame him for his influences, so in a sense we are to blame too. because we have fallen for Satan's influences and his sinful charm.
Just remember what Jesus did at the cross. the price he paid for our sin, and God went to the depth's of hell to take the keys, and all Satan's powers. So who is the weak one now? however, he still has the power of influences. and its that we need to watch for.