If you fail to plan, do you plan to fail?
In my experience dieting and coaching others, the answer to this question is: Mostly True. As the old man in A Princess Bride puts it, "there's a very real difference between Mostly Dead and All Dead."
So, it's not All True that you'll fail- it's still possible to make good decisions without a plan, but if you are in the early or rocky stages of developing healthy habits (and not planning your meals or workouts ahead is an indicator that this may be where you are at), then it will be that much harder to make or find or choose something healthy when you are out and about without a plan for what that is. Planning ahead will help you avoid one of the major pitfalls to Dieting: making a poor choice because you either didn't see a healthy option, or didn't find the healthy option appealing in the face of your the temptation that resulted in your poor choice.
Can you see the logic now?
But, I'm calling myself out because I am in just such a bind at the moment, already hungry and out of healthy snacks in my bag (plan a: to restock tonight); water (plan b: refill bottles ready to go at home tonight); and a good lunch option when I get home (plan c: make a healthy choice at Starbucks drive thru right now and plan meals for the next 3 days when I get home). A variety of unexpected events lead to this predicament, and now I have plan a, b, c to resolve it!
In closing, I'll unpack plan c: I have a few go to options at haunts that I frequent, and Starbucks is one of them. If I'm watching my weigh in, I know that a strawberry soy creme frappucino and a reduced fat turkey bacon egg sandwich has the lowerst sodium- if I'm not worried about the sodium, I may elect to go with a different 400 calorie sandwich, or a 500 calorie and a coffee with no sweetener and fat free milk. Do you have a plan for what to eat when you are out and about? Inevitably this will happen, so if you want to keep your dietbet winning chances Mostly Alive, I suggest you plan for when the plan doesn't go your way!!