We al know the mind can directly affect what the body chemistry does (transfer of blood to certain parts of the body when eye-candy comes along, triggering of fight/flee adrenalines, release of endorphins in certain circumstances, even widening of the pupils when we see something we like). It seems a not-unreasonable leap to think that a "positive mental attitude" might well help speeding of recovery from injury, and there have been numerous tales of it doing just that - although unproven scientifically (and how one would double-blind trial that would be interesting!)