Return is directly correlated to risk, so when a black box corporation is promising 15% returns and marketing itself as a “simple and safe” way for its users to benefit from “advances in financial technology.” It's probably not safe, but it is very simple.
This is at least a weak EMH assumption. It's not a law. In crypto sometimes the opposite is true for short to medium periods of time because uninformed people are afraid of 'too high' returns. Best money is made on market inefficiencies like that.