Well I'm no expert on motivation, I lose mine all the time. But when I DO get motivated even if it's a brief time it's usually because I can see a result quickly. I know that I'm an instant gratification kind of gal. So seeing that 3 pounds or even 2 come off gives me something to go on the next day. I have not lost anyone in my family to obesity or related health issues stemming from that, but my motivation in other cases is just the feeling good that comes from taking care of ones self.
For me, the weight and my love of food is a combination of:
1. I love the taste of food
2. Habit
3. Lack of self esteem
If I can combat those through various techniques it will help me in the long run. It's a day to day effort
Hope this helps some.