The absolute certainty that you are going to go off your diet, and
The conviction that a single screwup doesn't mean you're a failure.
I know (because I've done it...) that what happens is that you'll have that Whopper and then blow it all out of proportion -- "OMG, I'm the biggest f*ckup alive, I can't believe I ate that, what the hell was I thinking -- well, the diet's blown and I feel terrible about myself now, I might as well eat an entire bag of Oreos too." But if you looked calmly at the points or calories or whatever, you would see that your diet can soak up the extra calories from the Whopper over, like, a week. That one event didn't *really* kill the diet. What killed the diet was beating yourself up over that single slip (and you know you're gonna slip -- no human being is perfect), and then compounding it by eating all the cookies to try to ease the guilt.
If it helps, you could think of your eating plan as a practice, like a yoga practice. Nobody expects to be perfect at yoga when they first start, or when they first take it up again after some time away. You're practicing doing the poses every day -- that's why they call it a practice.
(It's very easy for me to talk calmly about all this, when I'm not in the throes of it myself...
)
) I won't. Plus I decided that most of the lowfat ones taste like crap. So I usually buy Turkey Hill Philadelphia Style, which doesn't contain any ingredients I can't pronounce. 
These days the stress has been sneaky. I am ok at work. But as I get home, thinking of all the crappy issues going on in my life I start to get hungers. By the time I hit my house I am in search of anything that is fried, salty or sweet. But last night I ate some turkey bean chilli and that seemed to calm the monster. Of course, between the chilli and the six calls from work last night I was up all night. 
. We always had a salad with dinner, even before it was trendy. She never allowed bottled dressing in the house, oil and vinegar would do just fine. But for all my mother's nutritional efforts, my father and his bagels loomed in the background. So my mother would give us half a grapefruit for breakfast and then my father would come in sunday with warm bagels, cream cheese, lox, whitefish, yada, yada, yada. I think, after a while, she just gave up.