There are some instances when you really don't want to do something. Maybe your sister wants you to babysit both of her kids when you'd planned to sit on the sofa watching Orange is the New Black all night. Maybe your neighbor wants to make use of your yard for additional parking for the party he's throwing on Saturday. Maybe your roommate wants to borrow $50. In many or all of these instances the natural temptation is to say, "I can't." That's not the truth. Actually, you can, but you don't want to. Don't say, "I can't." Say instead, "I don't want to." The latter is a statement of the determined force of your will. You are saying without a doubt that no matter the circumstances you don't want to. Your mind is made up. It can't be changed. Otherwise, you're saying there are outside factors that, if altered or accommodated, can mean that you will do what is being asked of you. When it's a matter of your decision to do something or not, make it known that it's your will that is making the decision.