Try this program, then tell me that you can never push yourself too far.
The average human being can not go without a day job, or live a stress-free life, or get 9 hours of sleep each night, or get daily massages, etc. All of those things would help deter overtraining, but you could still get it. It'd just require you to push harder. Much harder.
Steven Low can probably give a good explanation between the differences of "overtraining" and simply "overreaching." The first term is probably used too often where the second should be, but that doesn't mean it doesn't exist.
(No pressure, Steve. Hahah.)