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.
When you are lposing your motivation, go back to the very first step unto why you started something. The purpose of you continuing it. When you feel like you are loosing it, go back to your first step and find why you did it anyways.