A duty is an obligation, and this may be moral or it may be legal. A jury has a duty to consider all of the facts involved before deciding the fate of someone who is on trial. A police officer has a duty to protect and serve the public. Those who shirk their duty are viewed as unreliable and untrustworthy, and this is not how you want to be seen. Everyone has a moral duty to be honest and to help others when possible.
The first duty of a government is to give education to the people
It is the duty of children to wait on elders, and not the elders on children