[Life]Odd Expressions

You know, I was thinking about this the other day but: I was wondering where the expressions we use come from. I mean rather it be "The grass is greener on the other side, or beating a dead horse with a stick." It's obvious they came from some place. Every valid expression contains a little bit of truth to them but the main question is how did someone come up with them? For example "The grass is greener on the other side" was someone on the other side and found out it was greener or perhaps someone didn't water there grass on one side some year. Or perhaps the greener grass was on the other side of a hill, the side with shade and no sun.

"Beating a dead horse with a stick" well I suppose someone may have done this, why I don't know nor would I want to. Well anyway my main point is where do these expressions come from? And what was the actual situation they were created in? If someone would like post the answers on the forums today!