I would say Life itself is changed by motivation. Motivation is often gained in many forms,often by people who are close to us, people whom we work for and people whom we live for.
Commonly motivation is derived from parents,well-wisher, an achiever who becomes our role model and wise friends. In many organisations and some aspects of life the concept of reward motivates one to do better than the rest. For instance, an incentive in corporate offices or supermarkets (perform better,you stand to gain (appreciation or money or reward) often motivates people to work better. Healthy internal competition itself is a good motivator at work places and among school going kids (get first class, we will have a good holiday or we will buy you a cycle - these work well with young children).
Sometimes motivations comes from unexpected quarters, a difficult situation, when faced with adversity, here the setback for hurdles itself motivates people to have the confidence, 'Yes, I can do it'. Our critics and people who make fun of us at work and social circles sometimes make the best motivators, because of such deviant individuals, the affected person is motivated as never before to succeed in their endeavors and prove the critics wrong.
For me my father is the main motivator, now for my wife and myself, our children are our motivators - to do the best for them.