I was reading Soros' book, and he explains it in terms of his world, but it gave me an insight. Markets approach efficiency as a limit. They are never efficient, they are never done getting priced in. the facts on the ground are always real in the moment, but the information doesn't propagate as fast; there's latency. In some situations that latency is great enough that it can be capitalized on. Generally speaking, if you can glean any information from the future and have information assymetry you can pry alpha from the either.