How do you know if you are becoming stupid?
It is not an easy question to answer. Spend six months eating badly and skipping the gym, and the mirror will tell you the truth. It shows you the weight, the decline, in plain sight. The feedback is immediate and impossible to argue with.
But the mind has no mirror. You can slowly lose the ability to think clearly, to focus, to reason through a hard problem, and see nothing at all. A body that stops training gets visibly weaker. A mind that stops working just goes quiet. The decline is real, but it is silent, and silence is easy to ignore.
Here is the part that matters, though, because it cuts the other way too. The mind has no mirror for your decline, and it has no mirror for your growth either. The same silence that hides you getting worse also hides you getting better.
So you can be getting sharper every single day, solving problems you could not have touched a year ago, and still feel completely stuck. Nothing tells you it is working. There is no number climbing, no reflection getting leaner. Just the same quiet.
And that is the real danger. In the gym, the mirror keeps you going. It rewards you, so you stay. But the mind gives you nothing to look at, no proof, no progress bar, so people quit. Not because they were failing, but because they could not see that they were winning.
So if the mind has no mirror, how do you ever see it?
Usually, the first glimpse comes from other people. It is a little sad, but it is the truth. You catch yourself watching someone make the same mistake you used to make. You sit in a conversation and realize you are a step ahead of where you would have been. That contrast is often the first sign that you have moved at all.
But here is the trap. That glimpse is useful for a second and poison after that. Stay in it, and it rots into something ugly. Look at the people behind you and you get a cheap sense of superiority. Look at the people ahead of you and you get quietly miserable. Either way you have stopped measuring yourself and started measuring the distance to someone else, and that distance will never make you feel like enough.
So take the signal and leave. Let other people show you that you have grown, then turn away from them to find out how much. Because the real mirror is not next to you. It is behind you.
Think about how you measure a child's height. You cannot see them grow. Day to day, nothing moves. So you back them against a doorframe, make a pencil mark over their head, and write the date. A year later they stand against that same frame, and there it is, the gap between this year's mark and last year's, plain and impossible to argue with. You never once measured them against the tallest kid in class. You measured them against themselves.
Your mind has the same marks, if you look for them. Problems that used to stop you cold and no longer do. Conversations that would have lost you completely, that you now follow with ease. Books that felt impossible a year ago and feel obvious now. You could not see any of it happening. But set against who you used to be, the growth is undeniable.
You are not stuck. You just have to stop measuring sideways, and start measuring back.