I think for 'that day', he means for the rest of the day. This is known as the daily stop loss. The point is to stop yourself from ever having a huge losing day. Some traders and hedge funds have monthly stop losses as well. For example Paul Tudor Jones said in the first Market Wizards he used a 9.9% monthly stop loss at that time. If his fund was down that much he would stop trading for the rest of the month.
It's difficult in the beginning for everyone has opinions of what's necessary, what's important, what's high quality, what's nonsense, etc. The difficulty is even compounded by the fact that each individual would have different results on any particular system because of their accumulated beliefs, perceptions & mindset - not to mention PSTD of prior trading experiences. You'll find loud mouths frequently say such-and-such system "doesn't work", is "bullshit", "scam" or whatever and while accurate description for some, that's not mainly because of the system. Older, wiser traders speak more in whispers than in bullhorns. Like it or not, discernment is the skill that you will be developing and it takes time - much, much longer than anyone purports it to be. Being selective and discerning will be critical, use the ignore & block function and curate what you are exposed to. If you start trading focused on your PnL instead of your performance, you will, most likely attach your actions to an emotional payoff. While there are exceptions, this approach, most likely, will lead to becoming a statistic of being in the "95% of traders fail" category. In closing, there is no holy grail outside of you. Your main obstacles will be managing your internal state of emotions, identifying limiting beliefs and reframing your perceptions so that you can tune into signal more than noise. The mental side of trading is much more influential than the technical side. A competent trader can make even a simple moving average system work, for they have built the "spectrum of differentiation" within their mind. It wouldn't have the same results as something with more data, or something that has a better cognitive model of encapsulating intra-day price movements, it's just a tool and the results depends on the mastery of the person yielding it.
I think after a loss we need to analyze the reasons, and it is advisable due to psychological reasons.
Yes, it is truly a daily stop loss and it can be elaborated by extending it to a monthly stop loss. Both aim to prevent huge losses. Thank you for sharing.