Most individual investors, whatever their background, don't want to cut losses because they're programmed since childhood with an aversion to... being wrong.
We all want to be right.
As a result, they sit, paralyzed, in losing trades far longer than they should, letting small (manageable) losses turn into huge (catastrophic) losses.
It's unsurprising, if you think about it. It's all in the programming.
Most professional traders, on the other hand, don't have this problem. In fact, they don't particularly care if they are right on every trade. This sounds crazy, but it's not uncommon for a professional trader to be wrong 75% - 85% - or more - of the time.
In fact, I remember legendary trader Dennis Gartmann explaining once that the more trades he was "wrong" on, the more money he made at the end of the year.