Good dates sometimes end in bad sex. Bad dates sometimes end in good sex. Even in a world in which dating apps can all but guarantee mutual attraction, the romantic endgame can be unpredictable. We understand, academically, scientifically, and intellectually, what humans look for in other humans — the who of the thing — but the how of the thing escapes us. Why do some twosomes work while others don’t? Because the doors of perception swing on their hinges, that’s why.

The sexual parts of relationships can be broken down into roughly two components: attraction and compatibility. These are two very different things. The former has to do with initial chemistry and is relatively predictable (For example: If partners don’t smell like they’re related or meet under anxiety-inducing circumstances, there’s data to show that attraction might ensue.) But the latter is deeply dependent on behavioral pattern recognition and strategic decision making.

Psychologists define sexual compatibility as the feeling of being close in terms of sexual beliefs, preferences, desires, and needs. Compatible partners understand and empathize with what each other want in bed and elsewhere (handholding is sex too). The interesting thing about this is that sexual compatibility is often a product of mutual mythos. What’s even more important than how sexually close partners actually are is how compatible they think they are. For sexually frustrated couples, this is great news because perceptions change. For happy couples, this is also good news, because virtuous cycles tend to stay virtuous. As a 2005 study in The Canadian Journal of Human Sexuality put it,

Sexual functioning in an intimate relationship involves an interaction between partners. Hence, it may be important to take into consideration not only individuals’ own perceptions of compatibility, but also the role that their partners’ perceptions of compatibility play in shaping individual perceptions of sexual functioning.

Interaction — and communication — is key to improving perceived sexual compatibility and, by extension, sexual satisfaction. Do you think you know what your partner wants? Do you think your partner knows what you want? Even more importantly, do you think you know what your partner thinks you want? This is mind-fucking and, it turns out, also the thing that makes actual fucking work — or not. The expectation game can be a libido killer in certain situations.

Science presents an appealing source of wisdom when the vagaries of sex leave us bewildered, but it doesn’t have all of the answers. Why does bad sex happen? Because our bodies are not particularly efficient communication machines and because we do dumb stuff. Sex is like poker: It’s not about the hand you’re dealt. It’s about playing the other player.

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