Their work is great. They rock user flows, iterate like crazy, have taste and know their way around a codebase. But despite all of that amazingness, they are not afraid of being wrong. It actually strikes them as impossible that they might be right on the first or second or even third try. They poke holes in their own work and graciously accept and genuinely consider peer feedback. They are unafraid of quantitative or qualitative data proving that their assumptions are wrong. In fact, they expect that and embrace those disciplines as part of the design process. They aren’t concerned with admitting I’m not sure, because it just means they’re not omnipotent. They judge their own work by how it’s used and not by how much time they put in. They don’t make portfolio pieces, they make useful stuff that, hopefully, changes people’s lives.