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.
Sometimes truth really hurts. When we were children we were full of dreams, a lot of plans. But as you said by growing up its like you were loosing it all. But I think it depends too to the ambiance where we grow up. It depends on the adults that grows us up. Life might give us tough times, even to the point where you just want to leave everything and go somewhere far away. But miracles happen. Especially for those people who dont give up. Sometimes we lost our desire to that thing. But please, dont lose your goal.