In my experience most mechanical and medical emergencies are also the result of "poor planning". e.g. Medical: riding too fast; too long; too tired; poor visibility; choosing a poor riding line (I've scars for that error) etc. Mechanical: equipment choice; equipment maintenance; riding line; speed etc.
I agree with this to some extent, but it seems as if people prepare as well as possible (that is to say, in a highly thoughtful and meticulous manner in general). Disasters happen, medical and/or mechanical.