You are right that this is generally true for my cats, unfortunately, one of our cats will periodically go outside the box for other reasons.
For two cats, we have three litter boxes that are cleaned daily, new litter is added every couple of weeks as the level of the litter goes down, and then the boxes are fully emptied and fresh litter added about every three months, and that keeps them mostly happy. Unfortunately, one of the cats will periodically pee outside the box even when the box is perfectly clean, and the reasons are many, and somewhat ambiguous.
Sometimes it's the litter. Either we're trying a new litter, or the manufacturer changes the litter, and the cat doesn't like the new litter for some reason.
Sometimes it's the environment. She's using the litter box and there's a sudden noise for some reason, and then she won't use that box again for a while. Not really a problem when we have three boxes, unless she's been startled while using all of them within a short period of time.
Sometimes she's feeling stressed out. If we rearrange the furniture, the seasons are changing (generally only going into winter does this seem to be a problem,) can't pay as much attention to her for a prolonged period of time, go on vacation, or bring home a new child, she's far more prone to peeing outside the litter box.
She never poops outside the litter box, only ever pees.
We've pretty much just formed a routine to minimize the peeing issues. We keep the litter boxes clean, we make sure we pay enough attention to her, and we try to encourage her to use her litter box at least once a day. If we haven't seen her pee in the litter box for a few days (does not mean she hasn't used it, just hasn't used it in front of us) we start to minimize the available options for her to pee in/on (easier than it sounds, she tries to find substitutes for her litter box, so anything box like, or that she can use to bury, like throw rugs.)