do one's duty

As someone who’s been working on a book about cowardice for over a decade, I know that it’s a slippery concept, but also that classical, linguistic and military tradition define it pretty clearly as the failure, born of excessive fear, to do one’s duty.

"I felt it was my duty to come. I certainly felt it would be an unpleasant experience, but that's not a good enough reason not to do one's duty."

However, it is not only virtuous to do one's duty, but it is also the duty of the individual to do his best.

To do one's duty sounds a rather cold and cheerless business, but somehow in the end it does give one a queer sort of satisfaction.

It's easy to do one's duty when one doesn't care.