20% of total doesn't seem that far off, when you count all the patients from the very beginning of this method of treatment. If you check the patients who had this done in the very early days of this program, the regain rate probably is much much higher than 20%--that is why you hear from those who have negative opinions of the surgery that it will fail anyway.
I imagine the rate is much much lower now, with the knowledge that good post op follow ups and support is essential in staying successuful, and so, surgeons an bariatric centers include post op programs for their patients.
So, if the failure rate was, say, 30% years ago, and is now 10%, that does average out to 20%. Does this make sense?
And yes, as Kelley points out, if you go about saying it's too hard, can't do no harm cheating once in a while, then you will set yourself up for not doing well at this. You need to keep tight control over yourself especially during the early stages, because it is very hard to set up new habits--and as you all know, surgery is only a tool to help you set up new healthy habits for yourself, and in the end, it is those healthy habits that lets you stay at your desired weight, not the pouch and bypass.
Also, about a 10% of the lost weight regain is expected after you hit your bottom weight. So, if you lost 150lbs, your surgeon will expect you to gain back about 15lbs. Now, does that sound so bad? I mean, it is best if you do not regain, but, you haven't regained all of the 150lbs back, either. If you can stay on top of yourself at the +15 from rock bottom point, that doesn't sound bad at all, either.