The first time I really laughed with a man who later became one of my closest friends, we were standing in a coffee line at a work conference and the person ahead of us said something inadvertently absurd to the barista. He and I, who had not exchanged more than a hello before that moment, lost composure for the same two seconds, over the exact same word. We caught each other's eye. Twelve years later we still talk every other week. People underestimate how much that single shared laugh was doing. It was not only bonding. It was a very fast, very honest sign that the two of us process the world along similar lines.

Humor is harder to fake than almost any other social signal. You can rehearse opinions. You can study taste. You cannot manufacture the timing of a real laugh. When two people find the same thing funny without having to explain it, what they are actually sharing is a way of seeing. They notice the same odd detail in a room. They register the same gap between what is being said and what is actually happening. Comedy lands because of shared attention, and shared attention is rare.

This is why mismatched humor turns into such a reliable warning sign. You can like everything else about a person, but if every joke needs translation, the relationship will keep working overtime. You will both feel a small loneliness even when nothing has gone wrong. You stop telling each other the funny things that happen during the day, because explaining ruins them, and once you stop telling each other the small stuff, the texture of the friendship starts to thin out. I have watched two relationships in my own life end this way without anyone ever raising a real complaint.

Comic style is its own quieter problem. Some people work in dry observation. Others prefer warmth and exaggeration, and a small minority live entirely in absurdity. Two people in different styles can still get along, but only if at least one of them is good at appreciating a style they don't naturally produce. The pairs who cannot meet in the middle eventually grow tired of each other in a way they struggle to name. They will tell you the friendship just ran its course. The honest answer is usually that one of them stopped finding the other one funny six years ago.

When humor compatibility is real, it does practical work in the relationship. It defuses arguments before they harden. It carries the friendship through long stretches of nothing happening. It signals affection without anyone having to be earnest. People with a shared sense of comedy can sit through most of the bad weather a relationship runs into, because they trust the laughter on the other side of it. They also tend to spend less time discussing the friendship, which I now believe is one of the better signs that the friendship is working.

If you find someone who reliably makes you laugh at exactly the things you would have laughed at alone, do not let the relationship coast. That kind of match is one of the most undervalued forms of compatibility, and one of the easiest to lose track of when life gets busy. You can go years without anyone else seeing the world the way the two of you do, and then realize you forgot to text them back for six months. Send the text. Tell them about the small absurd thing. The friendship is partly built out of those moments, and it needs them to keep standing.