I am not personally affected by the negative oil price event but was pretty shaken by it. Why shaken? Because I thought I was well-protected by my risk management rulebook as a trader from this kind of event but that turned out to be wrong. The main rules were; - diversification - small position - cut losses quick Even a small position in oil on that fateful day would have been disastrous if one bought at $0.50, price went down to -$37.63 and the brokerage software did not allow the trader to cut loss because the software was unprepared for negative price. If IBKR refused to make good on the client losses suffered due to the software problem, even experienced, conservative traders could have gone bankrupt. Negative oil price was unprecedented in the oil industry, so I won't be surprised this can catch even veteran traders by surprise. Given the unprecedented extreme movement, mean reversion traders placing a counter-trend trade that would normally make money in their backtest could have been killed by that single trade, even if the position size was conservatively small. If I had to add a new risk management rule, it will be something like this - Avoid placing trades against the trend for leveraged financial instruments with open-ended risk. This rule is not as applicable to stocks because stocks are unleveraged, risk is close-ended (price drop to 0 at worst) and value investing which mostly involves mean-reversion bottom-fishing is a proven strategy.