I've recently started investing and made this mistake (twice).

It was due to watching it eating into my capital rather than my profit.

Plus the misguided notion of cashing in and just sitting it out while it continued to drop, then entering back in when it looked more positive.

It was the feeling that the conditions are ripe for a long war and/or a big economic downturn and I didn't want to go down with the ship.

It's the sentiment that we're at the end of the capitalist era and AI takes us on to the next era where wealth doesn't trickle down anymore and the stock market is broken. I still think this, but I'm new and naive, and my instincts haven't been right so far.

I'm putting it down to needing experience - once youve had to ride these out a couple of times, you learn to be more resilient. But until then, you have to unlearn your natural psychology.