Notice something about this cat? That's right - she's three legged (her leg was amputated a month ago because of a birth defect, on the advise of a vet). She's currently being fostered and awaiting a permanent home, and watching her play it strikes me that what someone said is true, that animals do not pity themselves when they have disabilities or are in some way disadvantaged.
The other thing that strikes me is also perhaps that is what holds people back - we have an awareness of our short-comings/weaknesses and as a result we give up trying. Cats don't - and so they don't give up.