It's easy to start a weight loss program. Staying on it is the hard part.
We're programmed to avoid change. Find that comfort zone and stay there! But, if you want to lose weight, you have to change. You have to change what you eat, how you eat, where you eat, how you get more active, where you exercise, your daily routine, your habits, everything. We're often tempted to fall right back into that comfort zone, with a giant glass of chocolate milk topped with whipped cream and that huge plate of cookies while sitting in front of the television and zoning out all day.
You can overcome the temptation to slip back into your old, unhealthy, weight gaining, fat lifestyle, but it's going to take some motivation. Here's are some of my favorite motivation ideas:
http://www.kristensguide.com/Health/Weight_Loss/ways_to_stay_motivated.asp