Duty's a slippery term. (Okay, okay: get the giggles out now: Yes, "duty" sounds like "dootie.")
I consider it my duty to attend to the most important needs of my family. So do my peers. But some guys I know with will literally rearrange their lives and work schedules and sleeping schedules, to see their children perform in a school play, or musical performance, or sports performance. As for myself, I make the effort to attend if at all possible, but if I have to work, or sleep, then I'm afraid I'm going to miss some of their performances. They know this. They're disappointed, and so am I. But my duty to their needs often means attending to the duties of my job first. I'm not saying that my interpretation is the right one. I'm simply saying that there are reasonable differences to be had on the issue.
There are some interpretations that run to the question of duty in the face of danger. As we've discussed before, the question of whether an armed citizen should hold his position or search and destroy an active shooter comes to mind. I've friends on both sides of that issue. Frankly, my interpretation is that you should tend to the safety of those under your charge, and let others tend to the safety of their own*. If you're in a room full of people, and you're the only one armed, I think your first priority is to hold that room. If, on the other hand, you're a teacher who stepped down the hall to the copy room to run off some copies, your duty is to resume your station in the room full of kids whose safety you are charged with.
What of the captain of a sinking ship, who has dependant family at home, but crewmen yet aboard? That's a tough one, no? Best to figure your duty before setting sail, and to alert your family of them, too.
I recently chastised an officer about neglecting his Area Of Responsibility as a cover officer during a roadside investigation. Depending on your specific role in a given situation, duties change. I think of Jane Harrison (GC), who on this date in 1968 perished aboard a burning airliner as she sought to get every passenger off, including a disabled passenger who also died. Her citation for the George Cross ends simply with: "Miss Harrison was a very brave young lady who gave her life in her utter devotion to duty." Note that the citation doesn't say that she went above and beyond her duty.
Duties on some days are harder than others.
*But note: different roles change the duty. For the police officer, everyone that he can reasonably protect is under his charge. For the person who has requested an exit seat on a plane, many others are under his charge. Don't like it? Don't take on the duty. With long legs can come great responsibility. :)