Just remembered something I've seen extensively in backtests and live trading with respect to stop losses. Especially live trading

You buy some stock or ETF which "cannot fail" and it starts losing value. It drops 5%, 10%, 15% ... nerves get tense and it reaches 25% down from the point where you originally bought them. It's all Murphy's law for stocks from this point on and it goes like this:
1) If your nerves break and you sell the stock, with 100% probability it will bounce back to where you originally bought it and even climb some more. Starting next day with one large jump up. But not if you purchase it again, then it will drop down again below previous day's level, goto #2.
2) If you hold steady and go Warren Buffet on the stock and keep it forever, it will continue to tank to 50% and lower, as long as you cling to it. The moment you sell it however, goto #1.