By any standard, professional athletes need to have an almost blind-faith in their abilities. The other guy wasn't necessarily better, I just had an off day. Really, it's understandable -- one doesn't reach the highest levels of any field without complete confidence. However, as Dario Franchitti proves, there's a difference between belief and delusion.
In story in the Long Beach Press-Telegram discussing his return to open-wheel racing and the IRL, Franchitti explains his 2008 NASCAR flameout as the result of many factors, including his own unfamiliarity with the cars (last July, Chip Ganassi folded the team and fired 71 people). And while he nobly accepts some responsibility for his failed attempt to make a place for himself in NASCAR, Franchitti ultimately lays the aborted effort at circumstances beyond his control:
[U]nfortunately my entrance into NASCAR coincided with the downturn in the economy. That really hurt us - and eventually it caused the team to shut down. It was a hard thing to accept, but there wasn't anything we could do about it. The sponsorship just wasn't there.
Of course, no admission on Franchitti's part that finishes of 33rd, 32nd, 33rd, 33rd, 36th, 22nd, 32nd, 41st, 43rd, and 38th in his ten races might have had something to do with sponsorship not being there...