However its original cause, the thought, originate in the mind. The thought belongs to you as no other person can enter your head. Therefore you should be careful about the thoughts which enter your head. We can modify those thoughts, choose the good ones and admit the noble ones. Unless we want, no one can inject any thought into our mind and if we really want, then, no one can prevent it either.
Sin is an evil force.
An evil force is behind every sin. When any sin is active in us, we should realize that an evil spirit is trying to gain control over us. We must resist that. Sin occurs only when he yields himself to it even for a moment. A person who sins is a slave to sin.