Rare, but not impossible as implied by the use of 'rare.'
There have been studies to prove that a certain degree of solitude is, in fact, healthy as opposed to detrimental to one's psychological well-being. That said, is it not a personal flaw that leads one to be vulnerable in isolation? If you are stronger with others and the others are the 'wrong' sort, you have already violated the sanctum of strength in numbers anyway.