I think your work day should feel kind of like a workout. You should be able to take the train home and feel like you gave it 100%. It makes it easier to connect with your family or read or crack open a beer and binge watch Westworld. Because you know you earned it.
Social scientists call it “deliberate practice”. While most people’s days consist of what Cal Newport calls “shallow work”, the people who love their work instead pursue deep work, work that requires intense bouts of concentration. That concentration leads to much more rapid progress, which leads to mastery, which leads to passion.