Ok, lets put you into this situation,

' You're going to face a major examination- Stpm for instance, in a couple of months time but you dont seem to be that interested in studying nor had you been paying much time into revising your subjects'

Upon seeing this, your parents are really upset with your behavior and even with constant scolding, nagging, advice and even some beatings, nothing seem to work. So what your parents came up with is what we would call 'reward power'.

They made a deal with you, upon completing your examination, provided that you pass your exam, they would grant you anything you want. May it be a holiday trip or even a brand new car. So this indirectly triggers you to actually want to do well in your exams.

Therefore, before you even realize it, you are basically starting to revise your subjects constantly without fail. Now, you would even stay up till mid-night only to revise, plus, you had even sacrificed all your leisure time just to study.

Half a year later, you realized that you not only passed your exam but also managed to obtain a few distinctions. And with your parents little use of power reward there, it proves to be very useful !