I have read on here many times (from those much wiser than I) that the difference is... "commitment".... and I have come to completely agree with this concept.
Commitment will get you through when motivation will many times wane.
It takes dogged commitment and knowing reality that we ALL will slip, stumble or fall in our journey to a better and healthier lifestyle!
It was only when I realized that I have to make a life long change in my life and not just diet until I lose what I want and then go back to my old habits and way of eating that things really started to change for me.
If you fall, pick yourself up, dust yourself off and keep going ... thats what I envision when I think of commitment.