This is a statement which has been proven over and over again. Examples would be the many people who have been in an accident and told by their doctors that "You will never walk again." Yet they have said in their minds: "Wrong, Doc. I'm going to walk if it takes me the rest of my life." They will themselves to go through the pain, turmoil and hard work and - Lo. One day they're back walking again. They believe that if they will it, the way will open up for them. And so often it does.
Finding an answer to a problem that the majority believe is impossible to solve by willing yourself to never give up until you solve it. Where you determine with your willpower that a way will be found because you know in your heart that nothing is impossible.