Everyone knew in a company or an organization that for promotion and salary increment you need outstanding work. Yet only few work hard to achieve this goal. The only thing that holds us back is lake of motivation. Why we need motivation from external sources for things important for our successful and happy life? To understand this, you have to understand yourself.
Food, water, shelter, clothing and air are basic needs of human being. When you are hungry, you search for food by yourself. You do not need anyone to motivate you. Your body only push you for things which are directly related to your survival or passing on your gens to next generation.
Once you have food, your brain wants to conserve this energy for longer time. You were not evolve to waste your energy in perusing intellectual goals. You were evolved for better survival. Laziness is nothing but the energy-saving mode of your body.
After fulfilling your basic needs, you left with ambitions and desires. Desires are self-perpetuating. Whereas achieving your ambitions requires pain, suffering and hard work. Thus, for achieving your ambitions you need external motivation. Because, in this case, your body does not drive you. Instead, you (your intellectual conscious brain) have to push your body to achieve your goals.