I don't think this is quite true... for instance, is it possible to purge one's mind of all unreasonable prejudices (against) or biases (towards) certain people, ideas, etc.? To be completely objective and yet, at the same time, empathetic with one's fellows? No.
And yet almost every single major religion and almost all systems of secular humanism advocate that we at least try to do just that...
Objectivity and Empathy are perfectly compatible. And I suspect that the strongest point of contention here is how we define and discover what tasks are impossible. I'm, honestly, not sure what tasks truly -are- impossible. But, if you come to me and state, with whatever proof one may need, that this task is impossible, I certainly think it would be pointless and nigh inethical to actually attempt to perform said task.
Now returning to ideals that are impossible...
Should we play fair?
Should we be truthful?
Should we be kind?
Perhaps you answer that we should be these things when it "makes sense." But what if we compelled to do this when it doesn't make sense.
I believe ideals are often inherently unachievevable.
I think, one issue here, is that achieving ideals and performing impossible tasks are distinctly different things. I would say it is, in fact, a noble pursuit to attempt to achieve an ideal. While you may not be able to do as such constantly, by working to achieve it you can noticeably -increase- how often you do it. If that makes sense.. so by virtue of that, you can still step closer to achieving it. Impossible tasks, however, are by nature tasks that you simply cannot do. There is no measure of completion or nearness, it is simply a binary "You have completed this" or not.
No I turn the question on its head...
What is an ideal that you meet all the time?
If you object to "all the time," When can you achieve particular ideals you hold dear? How sure are you of those times?
If you take I will know when, when it happens for ideals, how do you know you aren't copping-out?
This is a hard one. I guess the easiest answer here for me is the ideal of Understanding, of Comprehension. I always make an attempt to attain as nearly complete an understanding of.. things.. as possible. In light of this, I am constantly questioning, always poking and prodding. I seek to achieve a systemic understanding of everything around me. In regards to all the time, I think this is kind of a cheating answer because it's mostly a subconscious process. And as far as times, any time I recognize a lack in my understanding, I immediately seek to rectify that lack.