Have you ever wondered why cats hiss at each other or at you? The reason cats hiss is to increase distance from a trigger. It's an aggressive but defensive maneuver.
Many reasons that cats hiss can be found in your environment. One includes visitors to the home. That's really a classic. Cats don't like having intruders in their space, so it's really common for them to hiss at visitors. Other things that cats hiss at are each other and at other people when they're doing things that the cats don't like.
For instance, if you're trying to groom your cat or give your cat a pill, but you hadn't taught your cat to tolerate that, you're very commonly going to end up with a cat that's hissing at you and then probably subsequently scratching. If you notice that your cat's hissing at you or other animals frequently, that's a sign that your cat's under chronic stress and you should really be addressing whatever those triggers are. The first thing to do is to stop doing those triggers, and the second thing is to gradually acclimatize your cat to those triggers in very small forms so that they get comfortable. You can do that by presenting them with treats or with play sessions.
And that's why cats hiss and what you can do about it.