Read Psalms 101:3  David said that he needed to be careful about what he saw.  David said in this verse that he would "set no wicked thing before his eyes."  When you see something wicked, you remember it, even though you don't want to.  Satan will come to you later and tempt you to remember what you saw.  And you will.  That is why you should be careful in the first place about what you choose to look at.  David goes on to say that he hates the wicked people.  He doesn't hate them, he hates their wicked ways.  And then finally, David says that their wicked ways will not cleave unto him.  That means that their wicked ways will not stick to him.  When someone throws a ball of mud at you, it splats and sticks to your clothes.  That is what David is talking about.  Just like you do not want mud to stick to you, David said that he did not want wickedness to stick to him.  Wickedness is just as bad as mud!