Most of the swing trading myths that hurt overnight traders are not wild claims. They are reasonable-sounding rules of thumb that were true in a narrow case, got repeated until the qualifier fell off, and now sit quietly in the back of your head deciding what you do at 9:31 a.m. That is what makes them expensive. Nobody loses money on a myth they actively doubt.
Below are seven of them, each paired with what the published evidence actually says. The point is not to be clever about conventional wisdom. It is to notice which of these you have been trading on without ever checking.
| The myth | What the evidence says |
|---|---|
| Gaps always fill | Fill rates fall sharply as gap size grows |
| A stop protects you overnight | A stop is a trigger, not a guaranteed price |
| The real money is made intraday | Overnight returns have carried most index gains |
| A high VIX means down | VIX is explicitly non-directional |
| 5 a.m. futures show the open | The cash open is set by an auction at 9:30 |
| More trading means faster learning | Persistence alone correlates with losses |
| Forecast accuracy separates winners | Sizing and consistency dominate hit rate |
Myth 1: “Gaps always fill”
They fill often. They do not fill always, and the difference is concentrated exactly where it matters. Published retail studies of SPY opening gaps generally find that very small gaps — a fraction of a percent — close during the same session the overwhelming majority of the time, while gaps of 1% or more fill intraday roughly half the time, and gaps of 2% or more fill closer to a third of the time. Methodologies differ, so treat the specific numbers as ranges rather than constants. The pattern, though, is consistent and it is the opposite of comforting: the gap most likely to be against you for real is the one least likely to hand your money back. If you want a sense of how this varies by instrument, we looked at how gap risk differs between SPY and QQQ earlier this month.
Myth 2: “My stop protects me overnight”
The SEC’s own investor bulletin on stop orders states the mechanic plainly: the stop price is a trigger, not the guaranteed execution price. Once triggered, a standard stop becomes a market order, and it fills against whatever bids exist at that moment. When the market gaps across your level overnight, there was no moment at which your price traded. You are filled at the reopen, wherever that is. A stop-limit avoids the bad fill, but at the cost of possibly not filling at all — which in a gap-down is arguably worse. This is the whole reason stop-losses fail overnight and why position size, not stop placement, is the real overnight risk control.
Myth 3: “The real money is made during the day”
This one is backwards, and the research on it is unusually consistent. Academic work on the “overnight drift” — Lachance’s 2023 study in the Review of Financial Economics among others — finds that cumulative overnight returns in U.S. equities have substantially exceeded cumulative intraday returns over recent decades, with the gap running on the order of a few basis points per session. Compounded, that is most of the index’s realized gain arriving while the exchange is closed. Economists still argue about the cause. But if you treat the overnight session as dead time you are sitting out, you have the risk-and-return picture inverted.
Myth 4: “A spiking VIX means the market is going down”
Cboe is explicit that the VIX is a non-directional measure: it estimates the market’s expectation of 30-day forward volatility, derived from SPX option prices. It says how far, not which way. A rising VIX into an overnight hold tells you your distribution of outcomes just got wider in both directions — which is genuinely useful information for sizing, and useless as a signal to get short. Traders who read it directionally end up fighting rallies during volatile periods, which is a specific and repeatable way to lose money while feeling well-informed.
Myth 5: “The futures at 5 a.m. tell me where SPY opens”
They tell you where sentiment sits at 5 a.m. That is not nothing, but it is not the open. Index futures trade nearly around the clock, while SPY’s official opening price is set by an opening auction on its primary listing exchange at 9:30 a.m. Eastern. Between your pre-dawn read and that auction sit four and a half hours of European close, U.S. economic releases at 8:30, and the accumulation of market-on-open orders — any of which can move the print materially. We walked through what actually sets SPY’s opening price in more detail, and the short version is that the overnight tape is a rough draft, not the final number.
Myth 6: “Trading more often makes me learn faster”
Chague, De-Losso and Giovannetti tracked 19,646 Brazilians who began day trading index futures between 2013 and 2015. Of the roughly 1,600 who persisted beyond 300 sessions, 97% lost money and only 1.1% earned more than the Brazilian minimum wage. Barber, Lee, Liu and Odean’s work on the full Taiwanese market from 1992 to 2006 reached a similar place: consistent profitability was confined to a very small fraction of active traders. Persistence, on its own, is not a learning curve. Repetition only teaches when something separates the trades — a written thesis, a recorded size, a reason.
Myth 7: “Better forecasts are what separate winners from losers”
This is the myth we are most exposed to ourselves, so we published the numbers. Our audit of 24 SpyTomorrow pressure readings found 14 directionally correct — a real edge over a coin flip, and nowhere near the certainty a reader might want. A pressure reading is decision support: it tells you how much overnight tension the tape is carrying so you can size and pre-commit accordingly. It does not tell you what tomorrow will do. Two traders working from the identical read will finish the month in completely different places depending on how much they risked when it was wrong.
A forecast tells you what might happen. Your position size decides what it costs you when it doesn’t.
A cheap way to find out which of these you still believe
Beliefs are hard to interrogate in the abstract and easy to spot in your own records. Pull your last twenty overnight trades and answer five questions honestly. Most swing trading mistakes leave a fingerprint here.
- When a gap went against you, did you hold longer than planned specifically because you expected it to fill?
- Have you ever assumed a stop would have protected a position you were holding through the close?
- Do you size overnight holds differently than day trades — and can you state the rule?
- Have you shorted, or refused to buy, purely because volatility was elevated?
- Did your losing months come from being wrong more often, or from being wrong in bigger size?
The last question is usually the one that stings. Traders who audit this honestly tend to find their hit rate was fine and their sizing was not — which is good news, because sizing is the part you fully control. None of these myths survive contact with a written record. That is precisely why so few traders keep one.
This article is for educational and informational purposes only. It does not constitute financial advice, investment recommendations, or a solicitation to buy or sell any securities. Past performance and historical data do not guarantee future results. All trading involves risk, including the potential loss of principal. Always do your own research and consult with a qualified financial advisor before making trading decisions.
