The only people I've met who have lost weight and kept it off effectively cut crappy carbs a lot, and included an exercise regimen. The actual dietary and exercise specifics varied a lot per person, as did the ordering (I know someone who lost 70 pounds via keto, and only on hitting his goal weight did he add exercise in, as well as loosen his diet and macros), but those were the consistent attributes to anyone who took weight off and kept it off for > a year.

I've also met plenty of people who yo-yoed just by "eating less", which is what the grandparent comment was claiming. No change of -what- they ate, no inclusion of exercise, just tried to calorie restrict. They'd lose weight, possibly a lot (depends on the person)...and invariably plateau, get frustrated, and put it back on.

Obviously this is not a random sampling, but there's definitely a pattern that emerges if you look at how people who have lost weight took it off and kept it off. And there's also definitely a pattern if you look at the people who have lost weight and regained it. "Eat less" is not helpful advice (which is what the parent post was responding to). It's not entirely wrong (exercising, as per the parent, helped them eat less at meal time. Restricting carbs also helps people eat fewer overall calories too), but it's not particular actionable as formulated, and it reduces weight loss to a "willpower" problem, which study after study has shown is doomed to fail, and also leads to all sorts of negative feelings along the way.