i had no idea about boundary setting until i went to therapy. my life before that was full of my feeling trampled on because i didn't know what i owned or the other person owned. i felt vulnerable and uncomfortable saying "no", etc. i learned healthy ways to establish healthy boundaries with others. it's a work in progress but knowing the tools to do this has made my life more contented.

What is a boundary?
In a physical sense, it is easy to understand that a boundary marks off where your property starts and where the neighbour's ends. You are responsible for your property but not for anything that happens on your neighbour's.
While not as easy to mark off, our emotional boundaries also mark off where our responsibilities start and end. Too many people feel out of control of their lives because they don't have good emotional boundaries.
Boundaries are like fences in that they keep bad things out and good things in....
http://ezinearticles.com/?How-to-Set...ries&id=560907