John 8:44 says, '[The devil] was a murderer from the beginning, and has nothing to do with the truth, because there is no truth in him. When he lies, he speaks out of his own character, for he is a liar and the father of lies.'
Every once in a while we have these thoughts in our head that try to discourage us. These are actually lies from the enemy saying things like, "You'll never make it. Just give up."
And sometimes we hear these lies from other people saying, "You're nothing but <insert mean comment here>."