Hiden cost of reward!!

Reward does sometime increase one's behavior.However there is something everyone should aware of: Reward may undermine the intrinsic motivation.

First of all, what is intrinsic motivation and extrinsic motivation?
Intrinsic motivation is you are being motivate to do something within yourselves, for example you read books because reading is your interest.
Extrinsic motivation is you are being motivated because of extenal factor, for example you read text books because your mother promise to buy your something afterward.

For example a girl who like to play piano join a music class, her mother then reward her by giving her money each time she finish the class. By the time goes by the girl may lost her interest toward piano.

Now after studying psychology. i finally find the reason why i lost interest toward studying cause my mother rewards me a lot. HAha....