I don't know how that 90% figure came to be conventional wisdom but I recall reading it in a few books on trading that were not published or authored by people who sell trading systems and the like so what would they have to gain? And of course it's not in any broker's interest to publish a number like that (they already hate those disclaimers) because that might scare even more new folks from taking the plunge. But if you have a great relationship with a broker, he might agree after having a couple of drinks
