If we designed doorknobs the way we design software, each one would come with a user manual.
They wouldn’t be guaranteed to work. You could spend hundreds of dollars on a new doorknob, only to find the handle doesn’t turn, and the manufacturer doesn’t offer a warranty.
Your doorknob would have options for direction of turn, speed of opening, and click sound, but not shape or color.
Most doorknobs would be sold without locks. You could get a knob with a lock, but it would be $10,000.
Each door in your house would need a different doorknob, depending on what year it was built. Doors from 1994 would need completely different knobs than 1993 doors. Sometimes you’d be able to put a 1995 knob in a 1993 door, but not always.
Modern doorknobs — made only for modern doors — would understand some voice commands, like “What time is it?” and “When did you last close?” But only from one person in the house, and the commands for opening and shutting would be different depending on which knob you bought and which door you installed it in. Most of these voice doorknobs wouldn’t have handles, at all.
Some people would lay awake at night, wondering if our doorknobs were getting too smart, and would one day rise up and kill everyone.