The first thing to know is that you are doing the right work. Is this the most important job you can do today?
The second thing to know is that you gave it enough time. Did you clear your schedule and nail this work? Did you fend off all distractions and stay focused?
The third thing to know is whether or not you put your heart and soul into it. Did you bleed onto this work?
The work is done when it’s been giving priority, attention, and color.