Every detail matters. Every single one.
You're in a pub. You meet someone you like the look of. That's how you'll think about that pub next time. It matters.
You hire a car for the weekend. The gears feel a little bit flakey, and the gearstick isn't quite where your hand wants it to be. That's why you won't buy that brand of car. Ever. It matters.
You visit a website. There's an unusual delay between pressing a button and getting a result. They've lost you. They're obviously untrustworthy. It matters.
Sometimes the detail matters more than the big picture even. It's not just about presentation or perfectionism. It's about attention and assurance.
The only get-out clause for brands who get it wrong is that people might not recognise that it's your fault.