It can go the other way, though, too.

I'm a partner in a digital agency and used to think that if I dressed better, we'd sell more work.

The inverse turned out to be the case. We actually lost one potential job for looking "too corporate" (their words). Recently, our largest client noted something similar: that they sort of expected to see me in a hoodie, and would feel weird if I showed up in a suit.

The point isn't to look sloppy. Instead, it's to make the clothing something that they don't even think about.