I hate when people say things like "If only I had (this or that), then I would be succesful/happy/fulfilled,etc." No one is born into a life of perfect circumstances. Everyone who appears to be happy/succesful,etc. had to work through some obstacles at some point to get to where they are. No one's life is completely filled with happiness so if a person appears to be happy it is because they have examined their life, worked through their problems (which takes a great deal of emotional energy and will) and made the conscious decision to appreciate what they have and go forth in life with a positive attitude. If everyone made the most of what they had as this quote says, everyone would realize they have a lot to appreciate. They may even realize they've been taking some things for granted and it would be a very eye opening experience.
Personally, I try to be appreciative of all I have, although I know at times I take certain things for granted when I shouldn't. It's just very important to remember that when you get down, you need to take a look at all you have and not allow yourself to feel like a victim, but appreciate the little things that add to your life.