Ask a player about their worst mistakes and they will describe a spectacular bluff that failed or a big call that was wrong. Those are memorable and they are rarely where the money goes.
The expensive errors are small, repeated, and forgettable. That is precisely what makes them expensive, because nothing about them prompts a review.
Playing too many hands
The first and largest. Every marginal hand played out of position produces a series of difficult decisions, and difficult decisions are where a small edge turns into a small loss.
The cost does not appear as one bad session. It appears as a winrate a couple of big blinds lower than it should be, spread across every hour, which is invisible without tracking and enormous over a year.
Offsuit hands with gaps, weak aces from early position, and any hand played because folding was boring. Those three account for most of it.
Calling rivers on hope
The second largest, and the most avoidable.
In a loose-passive pool, a river bet or raise from somebody who has been calling is value nearly every time. Bluffs at that node barely exist. Calling anyway because the pot is large and the hand is decent is a leak that runs all session, every session.
The correct habit is to name a bluff they would take this line with. If you cannot name one, the call is not close. Our piece on river calling works through the arithmetic and the population read together.
Staying at a bad table
This one costs more than any strategic error and it is not a strategic error at all.
Games change as players come and go. A table that had two recreational players an hour ago may now be four regulars grinding each other, and after rake that game is close to unbeatable regardless of how well you play.
Most players stay out of inertia. Checking the table every twenty minutes and leaving when it turns is worth more than most of what people study, and it is covered in reading a table quickly.
Playing the same way against everyone
A single strategy applied to every opponent guarantees you are wrong against most of them.
Against a station, bluffing is a donation and thin value betting prints. Against a nit, stealing prints and value betting thin does not. Against a maniac, you widen for value and let them bet into you. The same hand in the same spot has three different correct plays depending on who is across from you.
Players who never adjust are not playing badly, exactly. They are playing a strategy designed for an opponent who is not at the table.
Ignoring what the game costs
Rake at low and mid stakes is proportionally the heaviest in poker, and most players have never checked what theirs is.
Two players with identical strategy can finish a year on opposite sides of zero because of the arrangement they play on. That is not a small effect and it is the only one on this list that can be fixed in a single conversation rather than over months.
Chasing losses
Adding tables or moving up after a losing session is the most reliable way to turn a bad day into a bad month.
The reasoning always feels sound at the time, which is the problem. The defence is mechanical rather than psychological: a stop-loss in buy-ins, set before the session and checked between hands rather than during them.
Confusing outcomes with decisions
The subtlest one. A hand that lost is not evidence the decision was wrong, and a hand that won is not evidence it was right.
Players who judge by results learn the wrong lessons in both directions: they abandon correct plays that lost and repeat incorrect plays that won. Over a year that produces a strategy assembled almost entirely from noise.
The fix is to review decisions rather than pots, and to judge over quarters rather than sessions.
What this looks like in our clubs
Across the clubs we run, the gap between a player who breaks even and one who wins steadily is almost never technical knowledge. Both usually know roughly the same amount.
The difference is that one of them checks the table before sitting, keeps a stop-loss, knows what rake they pay, and takes notes on the regulars. None of that requires studying anything.
The other pattern worth naming: players who complain most about running badly are usually playing the most hours at the least selective times. That is not variance, and it is fixable this week.
Frequently asked questions
What is the most expensive mistake in poker?
Playing too many hands, especially out of position. It costs a small amount constantly rather than a large amount occasionally, which is why it goes unnoticed.
Why do I keep calling rivers I know I should fold?
Because the pot is large and folding feels like losing. The habit that fixes it is naming a specific bluff they would take that line with; if you cannot, fold.
How do I know when to leave a table?
When the weak players have gone. Check every twenty minutes or so, and treat a table of regulars at low stakes as unbeatable after rake rather than as a challenge.
Is it a mistake to play the same strategy against everyone?
Yes, and a large one at low stakes where opponents differ enormously. The same hand in the same spot plays differently against a station, a nit and a maniac.
How do I stop judging my play by results?
Track big blinds per hundred hands over quarters, and review decisions rather than pots. A losing hand played correctly is a good hand; a winning hand played badly is a problem waiting to repeat.
Where to start
Pick the one from this list you recognised most and fix only that for a month. Trying to fix all seven at once means fixing none, which is its own familiar mistake.
If the one you recognised was the rake, that is the quickest to close. Message @supremaunion and ask what you are actually paying.
18+. Play within your means.