Willpower comes down to just one choice: do I choose to do it, or choose not to do it? Make it a concious decision. Being truthful to yourself, which will give you the better outcome? Once you start making these decisions and seeing the results, they get easier and you understand better what “willpower” is.
Looking objectively at “willpower” in this way helps you to remove the emotional attachment, and enables you better to choose “no” if that is more appropriate, and understand why you are choosing “yes” – and the consequences of doing so.