Where a house stops working for the people in it
Falls rarely come from one big hazard. They come from small ones that line up: a tub wall to step over with nothing to grab, a polished floor in the bathroom, a stair rail that ends a step before the stairs do, a door threshold with a raised lip, a hallway so dim at night that a person feels along the wall. Round doorknobs get hard to turn when hands stiffen, and a low toilet is a real effort on bad knees.
The most common mistake is a towel bar standing in for a grab bar. A towel bar is screwed into drywall and pulls out the moment someone leans on it. A grab bar has to be anchored into framing or solid blocking set behind the wall, and that's a carpentry job before it's a hardware job.