If you see a little child you can see the spark in their eyes. As we grow we keep loosing that spark. Life gets harder and keeps sucking the motivation out of us. I think motivation is the most precious thing in life and we loose it so easily without even being fully aware of it. As I grew up the most difficult thing I've faced is to keep myself motivated. The dreams we dream don't just come true. Our reality is totally different from our dreams.
The life of a child is different then the one of a grown up man, but still for a better motivation you have to do it like in gym, just finished the exercise and nothing else matters.