Yes the rule is correct, 90% of newbie traders lose money in their first 90 days in trading but it does not stop there. They will continue to lose money if they didn't acquire the right knowledge on their journey to become a successful and profitable trader to be among the 10% profitable traders in the trading industry.
The market works that way, it's a predator, not a prey like many think.
For those wise and experienced enough to profit, many others lose their depos due to different reasons.
So I do believe the rule of 90%, albeit the percentage may vary in reality.