For me it was "buy high quality pillow" because you sleep for one thrid of a day etc. I needed a new pillow anyway so I came to the store and bought the best they had. And it was ... ok. Like it's a fine pillow but my sleeping haven't improved really, it's basically the same. So I was disapointed :(
Also, although I agree with the sentiment, I only need a mattress that's just good enough to not cause issues, because when I'm asleep, I can't care about the mattress quality.