As I sit in the waiting area of a hospital, it gives the opportunity to evaluate people from an objective perspective. Everybody here is here for somebody else, everbody here has their own things going. Nobody is here for fun or just to pass the time.
The fellow next to me didn't get any sleep last night because of relationship issues. He's in a relationship with a quote: "much younger girl", he can't be over 30 and he descibes the relationship as exclusive, but there's another man involved.
So why am I telling you this? Because as a DM, crafting a new world, this is the kind of stuff you have to consider. You have to populate your world with people you don't understand, doing things you can't imagine doing, in ways that don't make any sense to you.
I can't provide any special insight into humanity, only that the next time you decide to start crafting your world, spend a little time at an ER/surgery waiting room, the local VFW post or a local college student union. Watch, listen, take a few notes, you'll be surprised at just how varied humanity can really be.