People lose money because the same people, like them, find the money somewhere. Nothing comes from nothing. If it has disappeared somewhere, it means that it has arrived somewhere. This is the law of nature, and no one can cancel it.
What do you have in mind? Obviously, money is a limited resource, and if someone has less of it, then somewhere there will be more of it, they circulate in this way in the global financial market.
But the question is why people lose money even in those moments when they should not do so due to their experience and knowledge in a market so full of opportunities.