You eat a lot and stay skinny. Here is the part nobody tells you.

What actually happens

Here is what actually happens. You decide to eat more. For about three weeks you do — big plates, second helpings, food when you are not hungry. The scale moves a kilo and you feel like it is working. Then a week goes badly. You get busy, or you get sick, or you simply stop noticing. The kilo goes away, and the conclusion you draw is that your body 'just does not gain'.

The boring reason

That conclusion is almost always wrong, and the reason is boring: you were never eating as much as you thought. Not because you lied to yourself — because a plate that feels enormous to a person who is not hungry is an ordinary meal to someone who is. Appetite is a terrible measuring instrument, and it is the only one most people use.

The part nobody mentions

The second thing nobody mentions: a skinny person usually burns more than they assume. If you fidget, walk a lot, work on your feet, or simply have the kind of body that runs warm, the amount you need is higher than the number you would guess. Two people at the same weight can need meaningfully different amounts, and neither of them can feel the difference.

The fix

So the fix is not more willpower, and it is not a supplement. It is one week of actually writing down what you eat — not to judge it, just to see it. Almost everyone who does this finds the same thing: a gap of a few hundred calories a day between what they believed they ate and what they ate. That gap is the whole problem, and it is invisible until you count it once.

Once is enough

You only have to do it once properly. After a week you will know roughly what your normal day looks like in numbers, and from then on you are adjusting a known figure instead of guessing at an unknown one. That is the entire difference between the people who change and the people who keep starting over.