How would you know? ;-)
For me, the most counter-intuitive thing has been the power of trend. Losers keep going lower, winners keep going higher. Markets over-correct most of the time.
Traders realize that efficient market theory is bullshit. XBI for example. Look at how it is impacted by Trump's tweets. Trading around 57 earlier this year and now 72ish on no news. It's just a biotech ETF comprised of hundreds of companies. How could market misprice it so drastically in such a short amount of time. Earlier this year, one could profit from XBI by shorting it, then bribing someone in the press pool to ask Trump or his press secretary during a press conference what he thinks of drug prices. Surprised no fund tried that.