Of course, the role of luck in market is huge. But among the sequential winners, you will tend to find people who win a bit more than 50% of the time. There's many opportunities to do something very stupid (e.g. invest in hydrinos) and lose.

Of course, the record is full of people who make money for years, only to explode later on (look at John Meriwether's career up until Long Term Capital Management blew up so spectacularly). Were these people always just lucky? We can never know. I take Taleb's point (filtered through Gladwell) to be that the base of people actively trading is so large that we should expect people who are successful for years (possibly even whole careers) even if all that is operating is luck, so past performance is no guarantee of future gains. I don't entirely agree, but its decent advice to keep in mind. Especially bad for the home investor is constantly chasing the funds that most recently made money (for some definition of recent)- generally the fees went up on the backs of the improved performance, so as performance falls back to the market value the investors will make less (lost to the higher fees).

Also an irony worth pointing out- Randy Mills of Blacklight Power/Hydrino fame has tried to create credibility for his company by pointing to the savvy investors who did get in board.