What was your "aha" moment?

Well, for me it was figuring out that not all calories are created equal. Sure, I could stay under my calorie ceiling eating pizza and small burgers, but I didn't lose very much weight. MFP is wonderful for tracking calories, but a lot of how much I do or don't lose from week to week depends entirely on what I am eating regardless of the fact I always come in under my calorie limit. Dropping the sodas --diet and otherwise-- entirely from my diet, and switching to water with lime or tea when I needed something with flavor helped. I stopped with pasta, cheeses, and anything cream-based as well. It took a while to get used to eating foods I would have considered bland before, but once I did and learned how to spice things up it got much better.

The Penzeys Spices are pretty much amazing for bringing 'zazz' to what would be an otherwise boring meal of vegetables with some meat for protein.

I guess there isn't a magic answer to the question that I can think of. Maybe someone else will have a better solution, but for me it was the change of more vegetables, less meat, and dropping all cheese/cream/etc. out of my diet that helped out the most.

I wish you the best of luck!

At 48 days here so far, I don't know if I'd fit your category of "sustained success", but I wanted to comment on this:

Well, for me it was figuring out that not all calories are created equal. Sure, I could stay under my calorie ceiling eating pizza and small burgers, but I didn't lose very much weight... I stopped with pasta, cheeses, and anything cream-based as well. It took a while to get used to eating foods I would have considered bland before, but once I did and learned how to spice things up it got much better.

The person quoted here has valuable experience, but just as a counter-point: essentially the only thing I've changed in my diet is my portion sizes and how often I have snacks of the same kind of food I'd be eating anyway, and I have not found this to be a barrier to progress.

I already had a pretty healthy diet. I still eat ice cream, occasionally eat pizza, fish and chips, and eat the same carbs. I doubt there is a day that goes by where I don't eat cheese in some form, and I drink full cream milk at times when I would otherwise have a larger calorie deficit than I am comfortable with. The main substitution is now using low fat instead of full cream milk on my breakfast. I already walked to and from work each day and still do. There isn't a single food I consider 'off limits'.

If anything, I've been losing weight a bit faster than most people here would probably recommend. Have set target at 1lb (i.e. 450g)/week, and trying to go 150-250 net calories/day under this most days after eating back exercise calories so that I can target 700g/week loss. This means on an average weekday I have a personal target of 2,290–2,390 calories to consume including those burned from my walk for my commute. (I am a tall male.) Experience over the last 48 days is I have lost 1.3kg a week on average. Presumably my base activity level is higher than I estimated.

For me it was planning out meals ahead of time and eating all day instead of just at meal time. I used to do two meals a day so by the time they finally came along I was really hungry and unprepared so I'd eat something easy (processed) and usually too much of it. I now cook nearly everything I eat and bring my lunch and snacks with me to work. I eat every 2-3 hours, even if I don't feel hungry. If I never let myself get hungry I never overeat. I only give myself access to healthy food and, thanks to not being hungry, I can stay clear away from the junk that people bring into work. I'm currently down 30 pounds from my starting weight but still working on the last 10 pounds.