Most will say untrue or during backtesting it did or did not pick up and one day scalping/ day trading only leveraged(and non leveraged) instruments you get the mother of all drawdowns. Stop and until figure out where system went wrong or system was right but have to adjust either cause of size of bars unlike what is your normal has changed abnormally, fat finger occurrence/news report, fluke tick, power spike, bug in pricing which transformed charting and platform in micro-second to read way different, exchange changed numbers to right of decimal, data stopped transmission, brokerage errors, breakdown in feed incoming/outgoing, speed of feed has slowed or become intermittent, equipment freeze, local holiday/world holiday & reduction of hours. We all like to think we have covered abnormal price action first in brainstorming phase and ongoing, but I am human no matter what others say. And why the need of redundancy allow your flow chart of your business depending on overall profits to reduce drawdowns. Also, changing one view of trading from making most profits to least daily drawdown can overall change to increase share/lot size. But the number per year/decade do not reduce in some ways, it is unaccepted form of trading as just matter of time of exceeding your worst nightmare drawdown for a day or number of days/weeks, months which has been proven in journals of many who have tried and failed to not make changes. Trading is ongoing business we have to be able to adjust to fluke or continue changes. Play the game long enough, some problem shows up unexpected. We all say "this will never happen to me" and the amount of traders filing bankruptcy and their kids now going to public school never changes. Protect home front by keeping emergency funding to not be touched and business funding separate. Hey very good suggestions in this post all.
No question you need to learn from mistakes. In my opinion, you should apply the same level of learning depth when it comes to positive experiences in the market. Learning what you do well and repeating it is crucial in my opinion.
To each his own, but I prefer to only be in one day trade at a time. Have you ever had two or three girlfriends at the same time? What a hassle!