Actually Moppie I was speaking psychologically, humans absolutely need interaction (preferrably with other humans) to stay sane (sorry for not making that clear). I suppose it's one of those basic laws of nature, once you have a skill you get an instinctive drive to use it. Humans have a gift that seems to be 99% unique in the animal kingdom, we can project ourselves into the minds of others. And no I don't mean some sort of ESP, I mean that we can see situations and ideas from another's point off view, which is definitely one of our most amazing traits. Think of it this way... it's very easy to learn how to play chess. But what makes a person good at chess isn't knowing the rules or even strategies, it's the ability to anticipate your opponent's moves ahead of time. And this is only possible because we can literally jump into their skin and understand (to a limited extent) what they are seeing and how they are thinking, call it intuition if you want but it's a very real skill. We not only have the ability to see ourselves, we also have the ability to see others in a way most animals have no comprehension of (incluing small children, this ability develops as we grow).
In the case of mental isolation, humans either tend to go insane or invent other things to have interraction with to stay sane. Those monks who practice total isolation actually just dive deep into the minds and inerract only with their God, who's either a fictional character or a higher power depending upon your viewpoint. But the point is that we have a need to interract with soemthing outside of ourselves who is also intelligent, it's a coping mechanism for living in this world if nothing else.