Compensation

On a number of problems I see as the explaination for a bishop/ rook exchange as insufficient compensation. 

This is a specifical expample. 

http://www.chess.com/chessmentor/view_lesson?id=6231

Can someone explain why this is so.  Chris

but i also have a question, if an ending is educative, why right more then three moves in the chess mentor text?? i cant imagine that someone doing chess mentor can visualize like 10 moves, i know i shouldnt be lazy and use analyse board but still its very confusing if you also have to remember the last 10 moves that were played with chess mentor.

ok its not that easy your question, better wait for a master explaining it correctly.

My Mistake.  I would looking at the explaination for the other color so an exchange of a bishop for a rook is insufficient material.  I need to learn to read. 

ok its easy to see its not good but its hard to put it in words.