This question already has an answer here:
Since Donald Trump has started to impose tariffs and periodically threatening to impose more tariffs, we see that the stock market tends to go up and down. When the stock market goes down by a sufficient amount I put in money in my stock account (which my bank invests this money in index funds). Then I wait until the stock market recovers, I withdraw that extra money I had put in. I then calculate the profit made by this intervention (this takes into account the extra transaction fees). Having done this a few times, my conclusion so far is that doing this seems to be more profitable compared to always leaving that extra money in the stock account.
The question is then where the extra gains I and presumably many other investors are able to make, is coming coming from. Could it be institutional investors like pension funds who have to stick to rigid rules for selling stocks when the price drops?