Hmm it's the same question I first asked when I joined this site, but I soon found that 3FC is just full of motivation. You're surrounded by people who are trying to do the same thing as you, people who have succeeded and lost weight and people who have kept it off (and some who have had to keep trying). It just makes me feel much more normal, especially when I look at people's before and after pics, I think... wow I could be like that one day soon..
My biggest motivation is the thought that the numbers on my scale are constantly coming down... when I first weighed in at 264.5 I felt physically sick and the woman weighing me turned around and said "look this is the last time you'll ever have to see those numbers again". And I really believe it is because I've steadily lost weight since then.
Whenever you feel down or feel like giving up, come on here and speak your mind.... there's always at least one person who understands (most times there's loads of people which is amazing!!!)

good luck, you can lose the weight - just have a bit of faith, dedication and commitment and you'll be fine!