For example, you’re cleaning a room, your home or your apartment. And you find it defeating the purpose to dust things and wipe them down because, dust comes back anyways and eventually. It might not be as bad as it was or as bad as it could be, but you’ll always end up with dust and cleaning dust is just a grand waste of effort and time.
Dusting and cleaning does not defeat the purpose. You’re making the mistake of thinking that cleanliness is boolean… true or false. It’s not that it’ll just get dusty again, it’s that it will get more dusty, and then even more dusty, and then dustier still, and there is actually no real practical limit to how filthy a place can get. Cleaning resets the progress to a point where you can live again.
Now, there is a related cleaning story that could be called defeating the purpose that stuck in my mind. It’s a bit Luddite in nature, but does have a point. It’s a micro-story from inside the book “Mrs Frisby and the Rats of Nimh”:
That’s an example of defeating the purpose, where the thing you do actually makes it worse. A similar “defeating the purpose” is when a bunch of companies lowers wages to save money, making it so that people can no longer afford their products, meaning that they earn less money after all.