No kidding on weight regain! Blink your eyes and bam!
The most important thing I've learned in maintenance is that the body of a reduced obese person (what the medical/scientific world calls us) is not the same as a person of the same weight who was never obese. Our bodies don't react in the way a never-obese person's does. Because of the many, many biochemical and hormonal changes associated with obesity and weight loss, we're colder, burn fewer calories with exercise, have slower metabolisms, and gain weight faster than someone who was never obese (same gender, age, weight, and height).
What that means is that the rules of the "normal world" don't apply to us. Metabolic calculators are usually way off for us. We may look "normal" on the outside, but our bodies are very different on the inside. Every fat cell I ever had in my life, I still have. And they're all pumping out hormones to signal me to "eat more! get fat again!" An obesity researcher once told me that a simple blood test (for leptin levels) would reveal that I am a reduced obese person. I may look like a fit chick on the outside, but on the inside, I'm still a fat chick.
And I'm OK with it! Knowledge is power. If I tried to live like a never-obese person, I'd be constantly frustrated. Why do I have to eat less and exercise more than normal people just to stay the same weight?? Knowing that my body wants to weigh 257 pounds again, strangely enough, gives me peace of mind. Because I know that I'm different than almost anyone I've ever met and none of the "normal" rules apply. I know what I need to do to keep the weight off and it doesn't matter what works for other people or what they think about what I do.