Mechanism
Displayed depth is conditional liquidity. In fast conditions, quotes can be canceled faster than you can react.
A thick-looking book can evaporate when volatility rises or when informed flow hits. That is why 'it looked liquid' is not a defense.
The book is a snapshot. Your execution is a path through a moving target.
Microstructure note: stops fail most often at the same time liquidity disappears. That is not bad luck; it is structural. Your job is to avoid competing for fills in the worst queue.
- Prefer “don’t trade” windows over cleverness: rollover, open/close, data prints.
- Reduce size before you reduce stop distance. Size is the only lever that always works.
- Measure slippage by regime, not by average.
How it kills accounts
See depth → assume safe size → enter → depth pulls → price gaps → stop slips → loss exceeds plan → confidence breaks.
How it kills accounts:
- Edge looks fine in backtest.
- Live spreads widen at the exact wrong moments.
- Stops trigger inside noise, so you widen stops.
- Same size + wider stop = silent leverage increase.
- A normal spike becomes structural damage.
Rule that survives
Size for the book you will get in stress, not the book you see in calm.
If the strategy requires large size, test impact and fills at different times of day.
Treat depth as information, not assurance.
Rule that survives:
- Spread is a gate, not a footnote. If it’s abnormal, you don’t trade or you trade smaller.
- Assume worst-case fills in fast markets.
- Size is the adapter: reduce size before changing the stop model.
Example archetype
You add size because DOM looks thick. A headline hits, resting orders cancel, and your stop becomes a market order in a vacuum. You discover the book was conditional.
Tell: if the trade only works when the spread is tight and price is smooth, it’s not an edge, it’s a regime bet.
Deep dive
What to watch
Look for regime tells: widening spreads, thinning top-of-book, and increased price jumps per unit time.
Glossary: liquidity, market impact, volatility.
Field checklist
- Measure spread before entering. If it’s abnormal, you’re trading the wrong product at the wrong time.
- If volatility expands, reduce size first. Don’t “solve” it by widening stops with the same size.
- Avoid the predictable liquidity holes: rollover, session open/close, first minutes after data.
- Assume your stop may fill worse than your entry. Price the worst-case, not the brochure.
- If you cannot explain where liquidity comes from, trade smaller.