A main reason was that Checkov, as a student of Stanislavski's, disagreed with his teacher on that point. One day in class he (checkov) began telling how his father (Tim said father today, I don't know if he told it wrong or if you remember it wrong mike) was close to death at that very moment, and he proceded to do a emotional performance before the class using that pain. However a few days later Stanislavski found out that checkov's father was not near death and had not been sick in years. Of course, this angered Stanislavski and he had Checkov kicked out of the school, only to be re-admited shortly afterwards because he was such a good actor and they needed him. Tim didn't say anything about Stanislavski later changing his views on the matter though.