Pure arbitrage pretty much never exists. There is almost always non-zero risk of loss. Arbitrage transactions invariably have some execution risk, though with very liquid markets and electronic trading it may be arbitrarily small. Generally the liquid markets with the fastest trading are those that will offer the least arbitrage opportunities though so in reality greater profits almost always come at the cost of increased execution risk. It doesn’t seem a huge stretch to extend the concept to statistical arbitrage—you’re never really going from zero risk to risk, you’re just increasing from a very small risk to a larger risk and going from very reliable price correlations to less reliable ones.
Pure arbitrage pretty much never exists. There is almost always non-zero risk of loss. Arbitrage transactions invariably have some execution risk, though with very liquid markets and electronic trading it may be arbitrarily small. Generally the liquid markets with the fastest trading are those that will offer the least arbitrage opportunities though so in reality greater profits almost always come at the cost of increased execution risk. It doesn’t seem a huge stretch to extend the concept to statistical arbitrage—you’re never really going from zero risk to risk, you’re just increasing from a very small risk to a larger risk and going from very reliable price correlations to less reliable ones.