Wossname - I assume the first part of your question is rhetorical? If we don't know what caused the incident then there is nothing we can do to avoid it happening again, all we can do is to try and avoid similar known conditions.
As the air is very thin at altitude the auto pilot does a much better job of anticipating and correcting deviations from a required flight path, it works in milli second whereas the human is much slower. Hand flying at altitude is usually demonstrated in training just to show how clumsy it really is and how uncomfortable for the passengers too, (the pilots up front often have no idea how uncomfortable hand flying is for the people down the back where the resultant effect of every move of the controls is magnified many times over in the passenger cabin), I have been on flights when the auto pilot has failed and even between the two of us we could not deliver a really smooth flight at altitude.