Why it matters
Queue position explains why backtests lie about limit fills and why partial fills happen. Execution is not just price, it’s priority.
Operational use: this is how the market taxes urgency. When it appears, slow down or size down.
Common trap
Assuming “price traded there” means “I would have been filled”. Without queue priority, you might not.
Example
You place a limit sell at 1.2500 after others. Price taps 1.2500 briefly, but volume isn’t enough to reach your order. You remain unfilled.
Operational cue: if you can’t point to it on the chart, in the DOM, or in your broker logs, treat it as a story and trade smaller.
Notes
Quick rule
- If you see this repeatedly, you are in a different regime than your model assumes.
- Regime change usually means position size change.
- When in doubt: trade smaller, or don’t trade.