When I started in the late 80's there was only one company (Dow Jones Telerate) that delivered realtime data on an IBM XT. I had to pay $1,850 a month rent for that pc. Trading forex was with minimum a $50,000 account. In 1993 a bought the first version of Omega Research for $2,500 and another $3,000 for a PC. Also had to pay Esignal satellite feed $180 a month and install a satellite dish again $2,000. Nowadays you just need a PC, datafeed is almost for free and software is available for free too.
Lol, that was long ago before I started trading. Here in Europe trading really started with the dotcom rise and crash around 2000. Nowaydays you dont even need a PC, the kidz trade options from their Iphones lol. But on the other hand, with all that crap around, it is hard to see the forest for the trees. You can see it everywhere, people have a hard time to understand what really matters in trading.
That doesn't answer the question why he broke the rules. What emotion makes an experienced trader ignore his own well thought out rules.
There can be many causes: emotional moment period with high stress for other reasons maybe just had received bad news just had a heavy other financial debacle in a divorce etc... All humans can get in a situation where they decide to do just the opposite of what they did all their life. Even if this moment just last a few seconds, the damage can be done.
I live in Europe. Nobody understood what I was doing. Even bankers had no clue. I was the only private client in my country who had that $1,850 a month machine from Dow Jones. All the others were trading desks from banks. I was even beta tester for them for a while. I tested their newest version that was in fact a license of Omega research's Tradestation. I found that program in the US, bought it and cancelled my expensive $1,850 renting contract. So in fact being beta tester was the cause of my switch to a cheaper solution. No rent anymore, just a satellite dish connection, and later on with Tradestation 2000i an internet connection.
PRACTICE! Just like everything else, practice taking your looses. Go paper and take a bunch of small losses. It just might reveal some holes in your methods. Stops are feedback. Don't ignore this opportunity. I think everyone gives this high win rate method a try. Everyone abandons it eventually. Except HFT folks, Personally, a 50% win rate, 30% loss and 20% scratch rate works out for my R/R. Lastly, I think, learning how to take a loss is an under rated skill. Some would say it is more or as important as any other skill (entry, letting profits run etc.)