HUMAN POTENTIAL: The Cause of Suffering II
We learn fastest through pain. It’s what karma is all about. If you were to get punched in the nose every time you walk through a yellow door, eventually (if you have any sense) you'll learn to stop walking through yellow doors. If you burn your finger every time you touch a hot stove, eventually you'll learn to stop touching hot stoves. If you make yourself miserable for years (or lifetimes) when other people don't live up to your expectations, eventually you'll learn that it's your expectations -- not other people -- that are making you miserable.
When your expectations are in conflict with what is, you resist what is and this causes pain.