"How do I cry on stage"?

Crying on stage can be a powerful tool, but often times I'm so swept up in the story that I don't care (or notice) if the tears are real or not. There is a longing to cry onstage because some people think it expresses deeper emotion and is an intimate thing. The ability to cry onstage does not make anyone a good actor. A good actor needs numerous qualities and abilities. I'm sure if I did a little research I could find many fantastic actors who never shed a tear in a movie, play, television show, or otherwise.