Cooler is a situation in poker when you are dealt strong cards, but in the course of the game, you lose to an opponent whose cards turned out to be stronger than yours.
Consider the preflop cooler situations
The most common form of coolers is the clash of such hands as aces versus kings. There are many examples when the game turns out to be unsuccessful for one of the participants. The main feature of such situations is that both poker players act correctly by going all-in on the preflop. In case you don’t have too many chips (tournaments, Sit & Go, Spin & Go), you don’t need an extremely strong hand to face the cooler. In these situations, even AQ vs JJ match-up may be called a cooler. As a rule, the fewer players are in a certain hand and the smaller the stack size is, then the hands to which the term “cooler” can be applied may be weaker.
Postflop cooler situations
It is difficult to define which hands pertain to coolers and which are simply losing ones and may be avoided by applying the optimal game strategy. It also usually happens that a very strong hand loses to another very strong hand. This includes situations where the set loses to the older set, the nut flush loses to the straight flush and the full house loses to the quads. Since the game on the flop, turn and river already gives enough information, there is a small chance someone will fold a weaker hand, which is strong itself.
There are strange cases when good players fold in cooler situations (mostly against predictable opponents in special situations). Folding such cards is considered a huge mistake because these are the hands you make money on. Dropping sets and flushes is the worst idea in Hold'em.
Cooler hands usually lead to large banks and can change the game. If we lose a big pot in the tournament because of the cooler, as a rule, it means that we are almost fatally “injured” and rolling straight down. Instead, you need to forget about such hands, because it’s impossible to learn from such situations. We just can’t prevent such cases, so you shouldn’t spend time analyzing them.
It's safe to say that coolers have absolutely no relation to professionalism. In fact, an average player can’t cope with a certain state of affairs without emotions. A winner is usually in the euphoria and a loser goes on tilt and starts playing worse or is simply out of the tournament.
Given the nature of the inevitable situations, the position of players is symmetrical. It means that no matter who wins at a certain point, you cannot play out a hand well or badly as the cards play for themselves. Both players are victims of the cooler situation and only the lucky one gets the pot.
The bottom line: coolers were, are and will always be in poker. In the future, whether we are hostages or winners of the cooler situations, everything will stabilize since we cannot influence the course of events. The best thing you can do is treat them as calmly as possible.
Coolers in different poker games
Coolers increase dispersion, therefore you need to have an appropriate size of a bankroll to survive the hesitations since they cause a bad play.
In Pot Limit Omaha, coolers are a very common phenomenon due to a large number of possible combinations, therefore, the variance is quite high there. In Stud Hi / Lo, coolers are less common due to the combinations are limited and a feature of the pot to be split - as a result, the variance is not so large.
The ability to cope with coolers (and in general with variance) as well as the understanding of the nature of coolers is the main key to success in the game.