A nice, necessary, interesting question, and one difficult to answer. I have seen so many of these mentioned people, and yes, some fit your description, while others, once you speak to them, you come to realise that all are not roses, even if you can't put your finger on the problem.
Life is largely subjected to the laws of cause and effect; action and reaction; and generally we are where we are. Much of us are largely playing out our destiny or fate, but this again is a very complex issue.
I suppose I'm just saying that a perfectly seemingly healthy, intelligent and able-bodied man, may not necessarily be all that he seems to be. But yes, sometimes I wonder too. Higher blessings.