What is will power? I personally define it simply as mastery over oneself. First, there is a difference between pure determination and pure stubbornness. To be determined is to recognize one's shortcomings, assessing one's strengths and possess fortitude and patience in the face of calamity. On the other hand, to be stubborn is to continue one's efforts and ignore constraints of reality, even when it is obvious that one will fail. Trying to fly with only two hands and firmly believing one will succeed is an example, albeit an idiotic one.
Another point to note is that being determined does not always ensure a result. In medical cases where willpower is a placebo for illnesses, it can be considered as a stroke of luck. Lastly, the topic implies that everything else is separate from willpower. This is not always the case, the choice to act in a certain fashion is affected by the human will to an extent. Willpower can also be present in elements like wisdom, judgment and rationality; they don't have to be separate.