While I'm a firm believer that our minds have far more of an effect on our bodies than we understand (and vice versa), at the same time I'm not going to be jumping up and down saying that our frame of mind is all that matters. As has been said, a dude stabs you in the heart then no amount of thinking "close the wound close the wound close the DEAR GOD THIS HURTS!" will change the fact that you're probably gonna die, assuming you weren't stabbed next to an ambulance or in a hospital.
And, as some of you have been asking for citations, well, technology can only do so much for us at this point in time. A lot of what's being said and studied is from anecdotal evidence, or simply speculation. Oh, sure, we've done brain mappings and seen how our bodies react to certain stimuli or patterns of thought, and have made our theories out of the data gathered. Yet at the same time there are plenty of things we can't explain just yet.
For example, I remember seeing footage of monks in meditation, kneeling in the snow and wearing towels drenched in ice water, and you see clouds of steam coming off of their backs. Is that simply because of a radical temperature difference between their bodies, the towels, and the surrounding air? Could be, but normally when you put something cold on a person's back you'd see their body temp lower rather than rise. So could this phenomenon also due to their minds? Their intense focus on willing their body to be warm? Who knows. Until proven otherwise, both theories are valid, as is the nature of theories. Unless of course, we already know how this was done (clever parlor trick is always an option), in which case I really would love to hear it.
(And for citation purposes, the footage I'm talking about was shown on an episode of Through the Wormhole, covering this very subject. The title might have been the same, but it's been a while since I saw it. Still, it had a few other interesting topics should anyone want to look for it. It might make for some good material to discuss.)