Why are many actors, especially good actors, mentally or emotionally unstable?

I think Actors or performers in general have an 'equal slice' of all the problems we ALL do...PERHAPS with some added ones that are specific to their occupation. They just feel they must either HIDE their problems for fear of ruining their reputation because ALL EYES are upon them, OR they show their problems and are judged because ALL EYES are upon them. MOST choose to hide their problems rather than dealing with them for reasons we can all understand I suppose. And hiding something or NOT dealing with problems always backfires someday. If we could close our eyes and imagine what it would be like to NOT be able to go to the grocery store alone or AT ALL, or to go most anywhere one might want to go because your FACE is recognizable and instead of being able to have a 'good time' you are watched, photographed and scrutinized for ANY thing that some reporter might 'cook up.' What kind of personality would likely 'develop' with someone like this? They likely would become reclusive OR go the opposite way and become assertively BOLD 'playing to the audience' EVEN WHEN their is no 'performance!' I think of Charlie Sheen as I type this! Another 'evil' comes along with notoriety sometimes...or perhaps MOST of the time and that is a feeling of 'being better or ABOVE the level of other people.' Having the world watch your 'shows' and becoming FAMOUS does, I think sometimes go to the head of a person! POWER and GREED and a 'spoiled baby' attitude that projects that 'they MUST have exactly what they want because they are somehow special' is common I think with 'performers.' MOST will not say it as Charlie did, but MANY I think....THINK it. Putting someone on a pedastal usually ends with them thinking they BELONG there for some extra-ordinary reason!
Lastly...I think 'having to live up to a certain reputation or personna of who one truly is' WOULD BE MIND BOGGLING. We often do NOT get a 'true picture' of who an actor really is by watching what they do and what shows they are in, yet to keep their public 'happy' they must live up to a certain level of reputation and 'make believe!' Going through this world NEVER being able to 'be yourself' would surely make someone wonder OFTEN who they really are!!! And questioning who you are too much leads to 'losing yourself.' WHEN life kicks us DOWN and we 'lose ourselves' we have lost our mind and what it is to be a human being or individual. THAT would create a lot of mental, emotional and addiction problems ALL by itself.
I GUESS in this case the 'bad guy' is really US...the 'public' or 'fan' who do NOT allow these performers to be 'human' without 'judging them' and without DEMANDING superhuman actions???!!!
Blessings,
Bunny7

As a profession, it's incredibly stressful, demanding and is a never-ending series of rejections for almost all actors. For the vast majority, it's a question of applying for 100 auditions and maybe getting one job out of all of them. They never know where the next job is coming from, if they'll ever work again, and if they'll be earning anything from one week to the next.
Even top actors have to audition, and they get rejected too.
It's also hard to have a settled relationship with anyone, because you're forever having to travel or even move address to get to where the jobs are, you can't make plans for holidays or even trips home to see family because you have to go to auditions and shoots whenever you're told - even if it's at a few hours' notice. That wrecks your social life as well.

And for the famous actors, they have no privacy, no freedom to just go shopping or relax anywhere, and every time they appear in public looking less than perfect, the cheap magazines plaster their awful photos all over the front pages.
They can't trust anyone, because even close 'friends' are willing to sell private details to the press for money. It must be a nightmare.
And that's enough to make anyone unstable!

Cogito has it right. Also see my blog post on substance abuse by actors at http://www.theatredoconacting.blogspot.com

Actors, and especially American actors, often work by the way of 'Method Acting', a more advanced version of Stanislavsky's way. The actor, for example, has to play a basketball player in 3 months.
This actor will live like a basketball player to get in his or her role for the movie. (Stanislavsky's way asks actors to dig into their own emotional revue to summon up old feelings with certain situations).

The obvious danger of this might be that actors lose themselves in the process, after they've played countless roles. This is why I believe most actors are unstable. (leaving aside the countless paparazzi that stalks them day and night, making them a bit paranoid(maybe)).

I'm going to guess that it happens becuase of the fame that goes to their head (ie - Charlie Sheen thinking how high he is and god like he is). They beleive that everyone wants them and wants to be them. They are above everybody else. The public and agents etc. probably don't help this by buying into all of their bullcrap and buying all the gossip magazines etc and giving celebriteis everything they want and more like billion dollar paychecks. Probably also becuase of the pressure that tinseltown puts on them to act a certain way or look a certain way.

BECAUSE, YOU HAVE TO BE RICH OR CRAZY, TO WANT TO BE IN THAT ACTING BUSINESS.........SINCE IT SO DIFFICULT TO GET INTO IT.

HENCE: THE CRAZINESS. OF THOSE WHO TRY TO DO IT.

ACTORS FEEL LIKE THEY NEED TO IMPRESS EVERYONE AND TO TRY TO GET AWAY FROM IT THEY TURN TO DRUGS WHICH JUST MAKES THEM SICK AND GROSS AND CRAZY.