Wow, I just realized I'm been a follower and researcher of the four minute
mile phenomena for 40 years. Summer of 1977, read books about the UK great runners, Ryun, T&FN and so forth.
What gives? It's been stamped enigmatic few want to tread into the deeper
waters of 3:45 and under.
Theoretically, If Gerry Lindgren broke the four minute barrier at an AAU race in Jamaica, it could've opened doors. People forget that the two (Ryun) were once rivals the only difference and think makes the difference, is the focus and Lindgren wasn't too greedy and let Ryun have his day with the high school mile.
The combination of talent, motivation and determination of course all coupled with a coach makes or breaks one. The Lindgren's, the Danlelson's the Liquori's...hard work.
If you aren't on that track flat on your back after a mile, with the air being ripped from your oxygen depleted body, you did not try hard enough. That includes some practices. It's in the mind. If you can accept during those very hard quarters and especially when you are flat on your back and say, "I am not my thoughts, body or pain" you're halfway there -- to immortality.
And don't you forget it.
Also if you can look past the eccentricities of Lindgren, he does have a lot
of good advice on mastering that pain.
See and read, nibble the book, savor it, "Gerry Lindgren's: Book on Running" by The Shadow of Gerry Lindgren.
His thinking is suited to more focused runner. You will see.