The Marginal Participant
The marginal participant is, in my view, the single most important mental model for understanding price action.

Markets aren’t set by consensus. They’re set by the marginal participant.

When you lift an offer on the ES, you’re not trading against “the market.” You’re trading against whoever is sitting on that offer—the marginal seller willing to accept that price right now.

The person or algorithm standing at the front of the line.

That price is now your entry price. The marginal participant set it.

The marginal participant is not a fixed category. It is a role that shifts depending on market conditions. And the nature of the marginal participant at any given moment determines whether you face an insurmountable opponent or a vulnerable counterparty.