to translate this question into terminology that makes sense to me, i will change "demands" into "principles" and i will assume that "do think demand the impossible" is not a reference to the peter marshall book https://en.wikipedia.org/wiki/Demanding_the_Impossible
but is missing the word "you", and means to ask whether we think anarchists are asking too much (of whom? reality? ourselves? others?)...
My answer to the "too much" part of the question is a) yes, absolutely, and b) no, of course not.
why should we ask for less than we want?
And anarchist principles (as alluded to in the comments already) are varied, but i will say direct action, mutual aid, anti-capitalism, anti-institutionalized hierarchies (like the church). those are fairly classic.
if this doesn't answer your question -- do please let me know where i went astray.