There comes a time in a lot of talented people's careers when they seem to step over a line. This is the line that, once crossed, takes them from being a manageable talent, mostly eager to please (give or take the odd tantrum), into a know-it-all monster who only wants "yes people" around them.
Think of the stars you love. How many of them did their best work early on in their careers? My guess is that it's quite a lot. Early in your career you get great guidance, people nurture you and they tell you when to change course. When you become a big star with an entourage, pushy agent and an ego the size of a New York skyscraper, you don't take advice nearly as well or as much. "I'm a star now. I can do what I want".
Working at your craft is never more important than when you break through into the "bigtime". Stars with longevity seek out other talented people to work with and learn from so that they can constantly stay at the top of their profession. Stars who crash and burn tend to believe their own hype.
Alec Baldwin, who acts superbly in my favourite sitcom 30 Rock, has given Charlie Sheen some great advice. He's told him to "sober up" and apologise to CBS. I think he's right. Charlie Sheen is way over the line and he needs to learn, once more, how to take direction.... if it's not already too late.