Before revision:  Since orders impact prices, reconciling the persistence of the order flow with market efficiency is a subtle issue whose possible solution is provided by asymmetric liquidity  which states that the impact of a buy or sell order is inversely related to the probability of its occurrence.
After revision:  Since orders impact prices, reconciling the persistence of the order flow with market efficiency is a subtle issue whose possible solution is provided by asymmetric liquidity , which states that the impact of a buy or sell order is inversely related to the probability of its occurrence.