Your thoughts are the source of your willpower. The actions you take flow from your thoughts about them. Every step you take is through the use of your willpower. Every time you do anything, it is through the use of your willpower.
A person who uses his willpower to engage in meaningful goals will feel a great sense of victory and joy. This might be difficult initially, but in the long run a person who uses willpower wisely will live a life full of joyful accomplishments.
You have the ability to choose to be joyful when you use your willpower in positive, meaningful ways. There is tremendous power in mastering "joyful willpower," to joyfully do what is in your best interests to do.
([From Rabbi Zelig Pliskin''s book: "Taking Action" - pages 16-7] (Artscroll.com)