What is the one quality you look for most in an interview candidate? Why?

What function are we talking about? Skills should meet the function as well as someone should fit the team and strengthen the capabilities. In some case some less qualities on the one hand can be compensated on the others.

Exceptional communication skills are essential for most roles, and can lead to the development of other important qualities. The lack of communication skills can create a myriad of issues for someone trying to be part of a team, and actually decrease the value of other qualities.