One phrase that works *after the fact*, when you've recently
   been given information that _entirely_ changes everything you
   thought to be true. Your actions of good intention turn out to
   have had dire consequences and seen from the light of the
   current information, appear simply dreadful, even to yourself.

   The words of comfort are thus:

   "You did the best you could with the information you had
   available to you at the time."

   In other words, act boldly with what you know if you wish. If
   you are acting in "good faith" (I think that's the right
   expression), it simply means that "Yes you were right at the
   time with what you knew but were you to do it again, it would be
   wrong. Since you can't do it again, what you did was right but
   only for that time."

   I don't know if it's *impossible* to know things objectively;
   for then that makes "IMPOSSIBLE" into an objective bit of
   knowledge itself. Rather, I'd go with "it's objective enough,
   subject to revision but can be acted upon in full faith and full
   trust, for there is no way to be _more objective_ about it at
   the moment just yet". You can also choose inaction ("choose not
   to choose") but that choice of non-choice (fate) also has
   consequences.