I am going to ignore your comments and the video you posted since that is just ancedotal. Focusing on the paper you yourself cite:
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"Consistent with prior work on the performance of individual investors, the vast majority of day traders lose money. In the average year during our 1992 to 2006 sample period, about 450,000 Taiwanese individuals engage in day trading. There are thousands of occasional day traders, but in the average year 277,000 individuals engage in day trades in excess of $NT 600,000 per year (about $US 20,000) 2 and about 20% of these day traders earn positive abnormal returns net of fees (commissions and transaction taxes). Of course, some outperformance would be expected by sheer luck.
But luck is not the whole story. Our main result documents the presence of statistically and economically large cross-sectional variation in trader ability. In the average year, about 4,000 day traders are able to predictably profit net of a reasonable accounting for transactions costs. Specifically, we sort investors into groups based on their day trading returns in year y and analyze the performance of each group in the year y+1. We document that only the 4,000 most profitable day traders (less than 1 percent of the total population of day traders) from the prior year go on to earn reliably positive abnormal returns net of trading costs in the subsequent year. But, the stock picking ability of these investors is remarkable. The top 500 day traders (based on prior year ranking) earn gross (net) abnormal returns of 61.3 (37.9) basis points (bps) per day on their day trading portfolio, while the tens of thousands of day traders with a history of losses in the prior year go on to earn gross (net) abnormal returns of -11.5 (-28.9) bps per day.
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So we have 4,000 "most profitable day traders" but that should not be compared to the universe of 277,000 active daytraders as those also consist of people who try daytrading for a year, do some YOLO and then quit.
What's interesting is, the paper has identified "tens of thousands of day traders with a history of losses." So these are the traders who have stuck with day trading over the years and can't become profitable. This should be the comparison.
So 4,000 make it, versus "tens of thousands" who don't. Pretty good odds if you ask me. Higher than the acceptance rate at Harvard of 3%.