It's VERY hard to accept that your own anecdotal experience doesn't apply to everyone. Especially in nutrition/diet/exercise, where basically the only information we have available is anecdotal.

If only that were the situation.

There's the generalizing from the one example which is your own experience, and then there's the generalizing from the one example that everyone is telling you is the real truth.

There's a complex, highly socially supported mind-blocking ideology which goes way beyond generalizing from one example. One is the common belief that "it's just a matter of "calories in, calories out", which eliminates a huge amount of biological detail. Another is "I didn't say it was easy", which is a way of blurring out the huge range of the amount of difficulty involved.

There seems to be an underlying belief that everyone is in some sense really fairly lean, so that any apparent health problems caused by (or causing!) weight loss can be ignored in favor of the Platonic truth of the ideal body.

It's not just politics is the mind-killer-- so are status markers.