Steem has definitely been the fire in my belly as well. It's a site where you can almost see the direct result of your hard work. I've seen many people work harder than me and get rewarded much less than me so it's not a guarantee, but it's nice to have an opportunity that the rewards I receive is almost directly related to the work I put in.
I really like the engagment league for that reason. I used to think I was one of the hardest working people on the platform, but realized there are others that either work just as hard or harder than me, which just motivates me more.
You are right it is a huge motivational tool and it does question how hard you are working. I notice on certain days when I do less as it reflects in the rewards. It is a definite gauge on what and how you do things.