What sparks "grass is greener"?

The older girls are in London watching Charlie and the Chocolate Factory right now, so the little girl and I are out enjoying playgrounds. 

Words of the day are "Nappies" and "brill". Nappies are diapers and brill is slang for brilliant.

It's funny, as I talk to more and more people in the UK, I think it might be human nature to think "the grass is greener" on the other side. I've been thinking Brits are more polite, but the locals here are convinced that Americans are much more likely to hold the door for each other and say please/thank-you. I wonder what's behind that perception, I'm sure there's research out there on it. I wonder if there's a way to spark that perception even when you're at "home".

Few more phrases for you since I hear them a lot..."Give it a go" - givt eh goh - which means "try". "get on" - git ohn - which means two people get along, friendly, not the dirty definition as far as I can tell. "really" -reh lay- what you say when you're listening to someone and really interested in what they're saying, you say it as a question.