In fact, attempting to rely on your will power to keep the weight (fat) off of you for the rest of your life is a ticking time bomb - it's only a matter of time before something else in your life will distract you and derail you.
Don't get depressed, the real key is to focus on installing strategies in your life that will help you keep your new body (or keep making progress towards the body you want) despite the inevitable chaos that visits everyone's life from time to time.
Here's a typical example of a "willpower day" gone bad:
7 a.m.: Skip breakfast because you woke up late.
10 a.m.: You're sitting in a boring meeting and are hungry. There's a plate of pastries and cookies (because nothing energizes your staff like junk food) calling your name. You've recently dropped two dress sizes and use your willpower to resist the siren song of the cookie platter.
Noon: Work is crazy today and you can't leave for lunch and you didn't bring anything with you. Work orders pizza for everyone (because, again, nothing boosts energy and productivity like a combo of white flour and grease).
You look at the pizza. You tell yourself "no." You go back to work. You are dizzy. You find the pizza and gorge yourself on it, and you feel like a failure inside.
Since you feel bad you inhale the bowl of M&M's that the company keeps full at all times as a way to maximize employee health and productivity because "it doesn't matter anymore ... if only I had the discipline to say 'no' ... ugh!" As you know, this day just gets worse.
Staying "on the wagon" is a lot like winning a fight with your spouse. You can't win a fight, but you can avoid them and get back on track ASAP when you falter.
These are my five best strategies for avoiding fights with your stomach or eyes, and keeping (or continuing towards) the body you want:
1. CLEAN IT OUT
If it's in your house it will end up in your mouth. In the above example, if you did somehow manage to make it home without eating the pizza or M&M's at work, you're going to be exhausted and ravenous. If there is a pint of ice cream (or whatever your vice is) in your freezer, you already know what "dinner" is going to be. You can treat yourself to ice cream from time to time, but just don't keep it in the house as booby-trap.
You need at least two "standby" meals - one at home, and one near work. These standby meals are meals that are compliant with whatever nutrition program you are on. The one(s) that are for home need to be something that you keep in the fridge, and is quick, easy, and reasonably tasty. For me this is eggs and spinach (or some veggie). I can prep, cook and clean up from that in six minutes (I've timed it).
So, for the weeks I don't have any meals pre-cooked, and I have nothing else, eggs are my standby. Other people keep frozen fish fillets and some frozen veggies that they like, and they can season and cook that up in just a few minutes.
The standby(s) at work are something compliant and reasonably tasty that you can order from some place near work - preferably from someplace that will deliver.
When you are under pressure and/or hungry you end up with "decision fatigue" - your brain is too tired (starved) to make a decision. So, if you already have a go-to compliant meal you don't have to do any thinking or deciding like you would if you were ordering from someplace new.
3. HAVE A HOME GYM
This does not need to be its own room, nor does it need to cost a lot of money. You're going to miss some gym workouts, and you need at least some kind of backup place. My "home gym" is a few kettlebells (they fit in the corner or my closet if we have company over), a few bands and a foam roller. That's it, because that's all that my condo will fit, but when life kicks my butt I can at least get something done.
What I can do at home isn't the same as what I can get done at the gym, but it is infinitely better than doing nothing. (Yes, I own a gym, but contrary to popular belief, owning the gym makes working out way harder. And fitness professionals spend their time at work making sure that their clients are getting results, not trying to sneak in their own workout on someone else's time.)
4. BULK IT UP
Novelty isn't action. Everyone's heard this before, but most people don't do this. On Sunday, cook at least one recipe in bulk so you have something compliant to eat for the week for at least one of your meals. You don't need to cook five different dishes, but you need at least one to be there for you. Make sure it's something that will keep (not shrimp or fish).
5. HAVE A STASH
No matter how well you do all of the above you will falter at some point and find yourself at work on a crazy day when you're hungry and can't get any food for a few hours.
Keep a stash of non-perishable healthy snacks at work and/or in your purse just in case. I have a bag of almonds in my filing cabinet, and they've saved the day more than once. The things that seem to work best for most people are nuts, jerky, or ready-to-drink protein shakes.
Use your willpower to get the above simple things done, and then that discipline will pay you back with interest.