I head about 90% of traders will lose money and ultimately give up but I have never heard about the ninety percent pertaining to anything else. Newbie traders tend to lose all their money rather quickly but usually not almost all their money... Most newbies are not that bad, I hope.
It's more like a non-written rule than the one that can be arguably proven by charts and analysis.
Most newbies just don't manage the risks properly or are too hopeful for their depos to become bigger.