See, I tend to interrogate this question from an inverse perspective: it is impossible to please a the complete, unbounded set of the audience of all people who might potentially read a fic, so a fic that pleases a) its author and b) some significant number of the theoretically possible audience is sufficient to define as 'good'; as theoretical audience approaches infinity, the probability of pleasing a non-insignificant number of its members approaches one.

However, to be 'good', feedback must by its very nature please one specific person, that is, the creator being feedbacked; and the tragic, entropy-burdened nature of humanity is such that the writer of the feedback can never understand any single other being so perfectly as to be assured of pleasing them entirely; thus the probability of pleasing creator is always significantly less than one. q.e.d. good fic is much easier than good feedback.

:P