From Bokardo:

Ironically, the smallest bits of copy, microcopy, can have the biggest impact.

Microcopy is small yet powerful copy. It's fast, light, and deadly. It's a short sentence, a phrase, a few words. A single word. It's the small copy that has the biggest impact. Don't judge it on its size…judge it on its effectiveness.

One of the biggest misconceptions about the web is you just design it, and don’t worry about copy.

Copy has such a big impact, more so than design in some cases.