As someone who never reads manuals. This.

That dishwasher isn't designed to be self-cleaning -- it needs help. Clean the filter regularly. Maybe every other load depending on how you pre-wash.

Same vibe for a lint filter in your washing machine. I think many people check the dryer lint trap, but the washer also has one. And the dryer vent hose will collect lint.

There are air filters in your furnace, probably, that need to be checked too, not just the intakes in a few rooms; and the AC drain line needs to be cleaned occasionally or it will back up and make a water mess.

There are just a thousand maintenance tasks that we are presumably supposed to just know, but no one told us, and can become serious problems when they are ignored. As the world becomes more complicated, there are only more of these.