Hm, that sounds like a misreading of the Taoist texts to me, with respect to your own view. Your "duty" as, say, a teacher is something that your own personal inertia, societal inertia, or what have you, can lead you to perform, regardless of any chances of "success." That word success would not mean much to a Taoist. There simply is, there is not success or failure, there is just existence. I recall the bit in the TTC about how calling some things good makes other things become bad.
And I also recall this: What is a good man but a bad man's teacher? What is a bad man but a good man's job? If you don't understand this, you will get lost, no matter how intelligent you are. It is the great secret.
This to me says - hey - do what you're made to do. If you're a teacher, and it's in you to do that, go on reminding and doing anything else that a different kind of thinker might label "futile." Nothing is futile. You do what you are led to do, and no more. This is wei wu wei. Do you work, and step back.