I'm going to pile a few ideas in here. It will come back to diet and exercise, but first I'm going to define commitment my way:
Commitment is the decision to do something even when you don't want to based on a value choice at an earlier time.
Why is commitment needed? Well, it's needed any time the desire for something will vary by situation or over time, yet you can still identify the value for the long term. So let's look at how the idea plays out in another area: Romantic relationships.
What does it mean to be committed to someone? What does it mean to be in a committed relationship? It's very simple. Commitment is the choice to stay in relationship past the low spots.
Consider that commitment would not even be needed if your experience of the other person was 100% awesome 100% of the time! You would need no commitment whatsoever because you would just always be loving what was going on and would naturally choose to be with that person. That actually describes pretty well the initial stages of a great romantic relationship. It's 100% fantastic and you want to spend all your time with your new love.
Then one day your 100% perfect partner does something really annoying. Do you decide you don't want that relationship now? For most people, they have (perhaps subconsciously) made a commitment to the relationship after some time, and the bad will be overlooked because they know the good stuff will be right around the corner.
And there's the critical idea to commitment. It's designed to take you past the low spots because you know the good is still there. Think back to the first time your loving partner got in a bad mood and was unpleasant. Did you say "This is nasty, I'm outta here!" Probably not. You might have that approach with a stranger, so the same stuff that would push you away from a stranger will not push you away from your committed relationship.
If you look at relationships as having highs and lows, or peaks and valleys, then we choose the relationship for the peaks. Then we fill it in with commitment to take us past the valleys.
Looking at it that way, the fewer valleys and the more peaks we can create the easier it is to stay (and be happy) in the relationship. We work on things to try to reduce the valleys and increase the peaks. And intuitively we know that the relationship is more likely to continue if that's the case. It makes sense, because commitment will only carry us through so many valleys before we start to reevaluate whether it's worth it for the random and very occasional peak.
I love my wife with all my heart, but if she chose to act in such a way that it was a continuous valley, eventually I'd run out of commitment. There has to be some reason to get past the valley. Also, if she did something that was more like a giant canyon than a valley (picture hot monkey love with the pool boy), that single event would end my commitment. Too big a gap to cross.
Again, commitment is just the decision ahead of time to keep at something even when it is temporarily not what you would choose.
Now come back to diet and exercise. If you're going to commit to a plan for either, please consider how commitment works in a relationship. No sane person would ever set out to find the ugliest, most unpleasant partner possible and declare "I'm committed to you. It doesn't matter how hard it is to be around you, how repulsive I find you, how vile you are, I will stay with you no matter what." Yet I see people do that with diet: "I'm going to eat nothing but 3 quail eggs and roasted acorns every day until I wear a size 0."
Okay, slight exaggeration, I realize no one would eat that many quail eggs. ;)
The point is you need to find the diet and exercise plan that requires the least commitment possible yet still gives you results. Commitment won't make you do the eternally unpleasant, it will just take you past the low spots. Plan on commitment to take you past short periods of hunger. Plan on commitment to have you occasionally eat something that isn't wonderfully tasty. Don't plan on commitment to have you be hungry and eat food you don't like forever. That's a plan to fail.
So identify what really matters before you commit to it. Committing to nothing but grass fed rather than conventionally raised beef? Great. Doable. I might relax it a bit from there, but if you go the other way and commit to only eating grass fed beef from cows that were personally named by a loving rancher who gave them daily massages and tucked them in at night, you're planning to fail.
Find what works. Identify what works. Then try your hardest to make that SO FREAKING EASY that commitment is barely needed. Then you've got a darned good chance at sticking to it.
You wouldn't marry a troglodyte. Don't commit to an ugly diet and exercise plan.