Quote from achilles28:
The market is nowhere close to efficient.
Academics couldn't figure it out so they postulated a theory of market efficiency. And those that did, quit their tenure promptly and moved to Grand Cayman.
Research a glossary of famous short term traders who compounded a meager stake into a vast fortune. Statistically, that's impossible.
Consider also, the vast majority of volume done on every exchange/instrument (>90%+) is speculative.
That's key, right there.
Market efficiency rests on the sole premise buyers and sellers are motivated by a fundamental desire alone to hold or short an instrument. That every oil buyer intends to take delivery and every short, holds excess production. Yet, >90%+ of futures are CASH SETTLED.
Same with currencies. Calculate the total value of global trade done on a daily basis with a generous assumption made for international capital flows, and that number is a small fraction compared to overall daily volume (4 Trillion).
Speculators drive short term market activity. It's that human element acting to capitalize on other humans that makes the market predictable. Because predictably they get it wrong, time and again. Why does history repeat? Because humans don't learn from mistakes. And speculators are humans...
A traders job is to identify other traders mistakes and inflict maximum pain. The utility from this lends to informative prices. A secondary effect: execution costs are kept tight and markets liquid for investors.