Someone once asked Shorter why he hadn't written a training book and he said if he did it would only be about two pages long. Eventually I believe he did end up writing one that was much longer. Ron Hill once wrote short article about trianing and essentially said, "Do a lot of easy running and mix in a bit of faster stuff a couple times a week." Kenny Moore once wrote that "all training is simply a matter of creating breakdown and recovering." A friend of mine who once was third at Boston told me that running is the ultimate in simple sports but people insist on making it complicated.
Yes, all of these guys are now either geezers or corpses and training theory has become more, uh, "sophisticated" and maybe for people with realistic possibilities of making national teams or winning major competitions that sophistication can make the difference between third and fourth place in a trials race. But for at least 99% of the people who show up at a road race, that's overkill and I think even a bit pretentious. Most of today's runners just don't run enough to get to their full potential. They'll get better results if they listen to Ron Hill but they won't sound as cool when they're discussing their training with others.
And that's fine. Doubling the amount of time you spend running in a week to get your 5k from 17:00 to 15:59 or your marathon to 2:55 from 3:10 may not be worth doing for lots of people. But thinking about tempo runs, double threshold sessions and how to adapt them to lower mileage, short hill sprints versus longer hill reps, etc., when you're running 40 miles a week is like buying the furniture before you'e done building the house.