Actually, the answer's not quite as clear. I've had my own share of psychology classes, but even the science behind our decisions doesn't clear up exactly how to predict the actions of another. What I found from the incident was not a scarring childhood memory, but a predicament that I'd like to explore -- are rewards, punishments, or obligations better motivators?
We all know what a reward is. When we were kids, our parents would surprise us (or, rather, not) with gifts like a day at Build-a-Bear Workshop, a new toy, or maybe even candy. This would be a sort of trade-off for good behavior, working hard, or generally doing a good deed. As Pavlov discovered from his early 20th century experimentation, rewarding good behavior conditions the participants into continuing their good behavior. If you keep a person on the edge, hoping that something good will come out of doing a certain action, such as practicing piano, then they will theoretically be motivated to do their work. Unfortunately, this can also work vice versa. If the reward is given too often, then the participants will eventually take the reward for granted and start dissociating it as a motivator to continue their action. Thus, when the reward is taken away, they will essentially have to be "weaned off" to begin doing the action on their own. On second thought, not the most budget-friendly (or child-friendly) method.
Punishments, similarly, are also synonymous with our early childhood. Even I can remember being spanked for talking back to my parents, albeit in a totally non-abusive manner. Most parents recognize that yelling at their kids, taking away their toys, or threatening them with physical punishments can be a scare tactic to trick them into performing a certain action, again in this case playing piano. As common as punishment is among parents to teach their kids good behavior, the press hasn't had a great history with its repercussions. One notable instance that caused glaring embarrassment to a family was when Amy Chua's editor published her excerpt from her controversial memoir, Battle Hymn of the Tiger Mother. In it, she described how she had threatened to donate her daughter's stuffed animals to a local charity, refused to allow her to use the bathroom or go to dinner until she practiced piano, and called her "garbage." To the typical American family, these punishments may seem a bit extreme, but as she described in her story, different cultures have different approaches to the term "punishment."
Anyway, I always figured a punishment works until the kid figures out that his parents aren't the boss of him/her anymore. Then comes the stage I like to call "The Rebellion." At this point, which often occurs in the late teens, the kid decides that he would like to take charge of his own life. With an inverse variation in the strictness of the parenting and the extremity of actions taken in The Rebellion, kids will often exhibit such symptoms as uncontrollable partying, abusive use of new independence, naivete concerning making decisions, and an inability to tell when enough is enough. Though this is obviously a huge generalization, I'd like to think that punishments have their downsides too. I hope.
On the other hand (can I even say that? On the third side? By the way?), obligations are a means of motivation often ignored. As a Chinese, I can say that it is also a somewhat effective means of motivation -- at least, no more effective than the prior two strategies. Obligations require a prior understanding and loyalty to some source -- often the family or the parents. In Chinese cultures, we call this filial piety and it's often linked with the parents teaching the kids that they were raised so that when they grew old they could support their old man and lady. This was in the hopes that the child would grow up successful and with means of supporting his/her parents in the first place. Anyway, obligations could be in the form of, "Your mother cooks for you three times a day, you should be able to play piano for three hours!" or "Your father goes to work just to pay for your schooling, now go study that anatomy textbook!" You get the nudge.
Which strategy reigns? The world may never know.
On a side note, I tried to use the reward system with myself today, without luck. This is actually pretty sad -- second day and I'm already getting cravings! What those health blogs say is true, after all. Once you start, it's pretty darn hard to stop.
Breakfast: Greek yogurt, egg white omelet, sticky rice
Lunch: Turkey and lettuce wraps, chicken soup
Dinner: Salad, mussels, white rice
Snacks!: Guacamole, (Whole grain!) tortilla chips, mangoes, cantaloupe