If one idea makes order flow click, it is this one: in every trade, somebody was waiting and somebody was in a hurry. The one in a hurry moves the price. Everything else is detail.
Two roles, one trade
The maker places a limit order and waits. They add liquidity — their order sits on the book as something other people can trade against. They accept uncertainty about when in exchange for certainty about price.
The taker sends a market order and crosses the spread. They remove liquidity. They accept uncertainty about price in exchange for certainty about now.
Exchanges price this deliberately: makers pay lower fees, sometimes negative ones, because a market with no resting orders is not a market. Takers pay more because they are consuming something scarce.
Why only the taker moves price
A resting bid at $0.9950 changes nothing while it sits there. It is potential. The moment a seller crosses and hits it, a trade prints at $0.9950 and that becomes the last price. If the seller's order was bigger than that bid, it keeps eating downward through the book and the price falls further.
So when you read "buying pressure", the precise meaning is: the volume of trades in which the buyer was the taker. Not open interest, not sentiment, not how many people said they were bullish. Who crossed.
The inversion that breaks homemade indicators
Here is the part that bites everyone building their own tools. Most public trade feeds report the maker's side.
On Coinbase's public feed, a trade with side: "sell" means the resting order was
a sell — so the incoming trader bought. Take the field at face value and every
buy is logged as a sell. Your flow indicator will then be perfectly, confidently backwards, and
because markets are noisy it will look plausible for days before you notice.
The check takes ten seconds: on a day the market rose several percent, does your indicator say net buying? If not, you have found the inversion.
Different venues make different choices, and some report the taker side, so the rule is: never assume — verify against a day with an obvious direction.
What this changes about how you watch
- Volume alone is meaningless. A million dollars traded tells you nothing until you split it by aggressor.
- A flat price with heavy one-sided taking is a coiled spring. Somebody is absorbing it. When they stop, the move is fast.
- Big resting orders are not conviction. The maker can walk away. The taker already paid.
Seeing it rather than computing it
Once trades are split by aggressor, the market stops being a line and becomes two opposing forces — which is exactly how we draw it. Buy-side takers march in from the left, sell-side takers from the right, each sized by the dollars behind it, and the boundary where they meet is the price. Absorption looks like an army that cannot advance. A break looks like the line suddenly running across open ground.
Same data. Same public feed. It just stops being a spreadsheet and starts being a picture you can read at a glance.