All dogs fail, failing equals a bad day, whether they just plain get outrun in real tough terrain, strike a track they can't finish, terrible scent conditions or any of a myraid of possibilities. It is how often one has the bad days and what we will tolerate that makes or breaks them.
If I see it this way then no doubt…great dogs will have bad days…
I see it in another way per example…
A great professional running back might have a bad game for a reason or reasons…but we know he is a great running back…he did the best that could of been done by any professional running back…we can single out a game here and there and say ole so and so could have done better than the great running back….but when looking or comparing all running backs in the NFL in that particular year there will be a few that tend to do better than others regardless of conditions…
I see hunting dogs in the same way…