Many years ago I heard a professor who'd studied a wide variety of presidential campaigns describe the thinking of candidates the day before the election. He said that no matter how hopeless the race, near the end a delusion would capture both the candidate and the campaign staff, and they would think, however briefly, that they just might be able to pull it off.
That's one reason why, even if I strongly oppose a candidate, I hold a certain sympathy for those strange souls who've been living in motels, sleeping on strange mattresses, and dealing with sleazy reporters.
While the rest of us have gone about our normal lives, they have been standing outside factory gates at five in the morning while some people refuse to shake their hand. They have been delivering the same speech over and over again, often to sparsely-attended events. They have missed their families and friends and have gone for months always having to be "on" and weighing every word lest a legion of second-guessers savage them.
It's a brutal process and much of it has little to do with how they might perform the job. And have no doubt, the process itself drives off many potential candidates. That is our loss.