Never try to teach a pig to sing. It wastes your time and annoys the pig.
- Mark Twain

I am sometimes asked, 'Do you think of yourself as you think of the organisms you study?' The answer is yes. So far as I know, my behaviour at any given moment has been nothing more than the product of my genetic endowment, my personal history, and the current setting.
- BF Skinner

As you reward a behaviour, it is more likely to be repeated. This simple fact is the entire basis of Ivan Pavlov and BF Skinner's behavioural theory. While it is by far the easiest theory to prove and understand, it is critisised for being overly mechanical and comparing human beings to rats and pigeons.

This entire theory is incredibly simple: reinforcment tells you what to do, punishment tells you what not to do. There are two types of reinforcment, positive and negative. Positive reinforcment is providing positive stimuli, such as giving a child a treat. Negative reinforcment is stopping unpleasant stimuli, such as taking a child out of time-out for being quiet. Punishment is using an unpleasant stimulus to discourage unwanted behaviour. It has been proven that:

1. Reinforcment works better than punishment
2. Positive reinforcment works better than negative

There is only one more factor in this equation to take into consideration - on what schedule a behaviour is reinforced.

This perspective doesn't take into account the idea of human will; in actuality it doesn't seem to exist in the theory. Therefore it is hard for even scientists and the most empirical thinkers in psychology to follow only this theory.