What does it mean to be "tough" in UX

Hey Folks,
Longtime lurker in this community, first time posting. I recently got an intriguing piece of feedback from one of the scions in this field, a legend which has given me pause. The role required someone with a high level of toughness. In my mind, I do know what they mean in a rough sense. To essentially not be a pushover. Though, I'm still thinking, what does it mean to be a tough designer. What are the traits. Where does one draw the line, what's the balance?

What do you think fellow UXers! What makes a tough designer, or a designer tough.