There was a group of hackers in the news recently that hacked the SEC's repository of earnings reports and had advance knowledge of earnings for tons of companies. They were only able to profit 70% of the time. Matt Levine @ Bloomberg discussed it.
Profiting 70% of the time is pretty exceptional. Even with insider info like that I can't imagine anyone being able to consistently do much better. The few trading strategies I'm familiar with, you have an expectation that you probably won't even take profits 50% of the time, but that the risk/reward ratio for every given trade is at least 2:1, ideally higher. So you can profit even around 30% of the time as long you're cutting losses intelligently and only trading high-reward plays.
Agreed 70% is fantastic. But it's surprising that having information no other trader has doesn't guarantee that you'll make money every time.