It's not randomness is the problem, it's the negative expectancy.
You can have randomness, with positive expectancy, a random walk with a drift or trend, where the mean , the variance and the covariance (of the lag) is constant, but the random variable is random inside these boundaries.
For example a price going up in this way would be easy to trade and make money from. The closest thing that resembles this are probably financial bonds, but only if their interest rate is not negative, haha.
It's not randomness is the problem, it's the negative expectancy.
You can have randomness, with positive expectancy, a random walk with a drift or trend, where the mean , the variance and the covariance (of the lag) is constant, but the random variable is random inside these boundaries.
For example a price going up in this way would be easy to trade and make money from. The closest thing that resembles this are probably financial bonds, but only if their interest rate is not negative, haha.
http://www.investing.com/rates-bonds/euro-bund (monthly chart)
I agree. Was too quick in answering. Sorry.