Why we travel, part 2

Why do we travel? Sometimes I wonder, what's the real motivation for people to travel? Not weekend getaways. Not seven day holidays. I mean long-term travel, 2 months stints or longer. Seems to me, there's a mix between internal desires (to escape, to be self sufficient, test yourself, to prove that you can do this) and external ones (see new things, eat different foods, meet new people). Strange that the external motivations are 'new and different', and the internal ones really having nothing to do with tavelling, about where you are, only about who you are.