Today? At its peak in 2009, high-frequency trading firms generated over 60% of US equity volume. The figure remains near 50%, and their presence in futures markets is at least as significant. These firms make decisions based on patterns humans cannot perceive. They execute thousands of orders across multiple markets simultaneously, in microseconds. They use co-located servers positioned right next to exchange matching engines. They employ hundreds of PhDs and spend billions on infrastructure.

Call this the typical marginal participant: patient, unconstrained, optimizing for profit. You can’t outthink them on their terrain. You can’t out-analyze them. You can’t see what they see.