We often see actors complaining of being typecast as mere "action heroes" or "comic actors." that there is more to there skills than what the public has typecast them into. They would complain just for the sake of complaining to satisfy the inner urge of justice. Justice to the profession, and justice to themselves.
So, in Bollywood, as Sunny Deol continues to play the umpteenth someone in the umpteenth movie who can smash pillars to dust, he wouldn't react well if told that he has failed as an actor. It is what I guess is called "playing oneself."
In life too, we assume roles and accordingly, we play them. If you don't choose a character, your friends will assign you one. The world runs on the fuel of simplification which is used to detangle certain complex situations. Typecasting is one way of achieving this simplification.
If you are an angry young man, you cannot just wake up one day and start cracking hilarious jokes. It is out of your character. These are long-term deals. There is also something I call as "point typecastings"... or more accurately "instantaneous role-assignment."
If you are sitting with a group and among them, someone calls you a shy kid, you will, to a certain degree, oblige the comment with your acts even if you are one of the most chirpy kinds. This act of obliging is not voluntary. It just happens. This psychological tool is often used with hard to control, unruly children. Saying that, they are "good boys" or "good girls"... gives them an opportunity to change their image in front of the audience. It is another matter that kids have long deciphered this code language and have stopped obliging the orator and audience.
It is a nice thing, in my view, however, to understand this setting. If you know what is where on a stage, you can perform better, you can play more diverse characters, win more accolades. Likewise, in life, if you know which character to play, how to have a control over your character, and when to stop... you can win.
The last three words taken without permission from Mr. Shiv Khera.