I'll bite. It's been a while and my memory's fuzzy, but I want to share some of the training I did to run under the sub 4 equivalent in the 1500m. I did not run under 4:05 for the mile.
A bit about me: During my best years I was not bonded to a program, but rather 'did my own thing'. I had a coach who coached many other successful runners, but we didn't run together and only rarely did workouts together. The stuff we did was quite different from each other, although every single one of us put in significant mileage in training. I ran 14 times a week most of the time unless it's raining heavily or I have some special commitments.
I ran year-round, seldom taking breaks. At the start of my training block, I did 20 minutes am and pm, 7 days a week. This gradually grew to 45 am and 50 pm over 6-8 weeks. I ran the morning runs before breakfast and made sure to run slowly, so I can recover in time to maintain the consistency. My second run of the day was faster, done before dinner or after dinner in the summer months. I ran mostly by feel and did not keep a training log. I do my distance runs mostly on grass and dirt.
I believed in building myself up in training, and so I cut out or reduce the training that would break me down. I felt longer runs (>60 mins) break me down, so I rarely run longer than 50 minutes, although I would do this 7 days a week. I felt that anaerobic hard efforts break me down, so I didn't do those often. Mileage never broke me down, and I've never injured myself in training.
Before I PR'ed in the 1500m I put in 28 weeks of 45 am, 50 pm, which gave me a significant aerobic base. I did strides often and hill sprints often, but besides that and some progression runs there was no other 'quality' work. Eventually, I worked until I can run 14 or 15 ks in the 50 minute afternoon run, while still feeling easy and relaxed. Then I started some tempo and interval work, stuff like 8k in 25 mins and 3x3x1k in 3 mins w/short jogging rest, while increasing the frequency of strides on my easy runs. Mileage was pretty consistent during this period and did not go down too much. I raced some cross country and maintained daily 2-a-days.
During the racing period I still run twice a day, although the pace was slower and I did not run as long. I started doing harder workouts like 4x5x200s in 29, jogging 200 between reps and 5 minutes between sets. I'll blast a few 27s and even an occasional 26 at the end. I did not taper much, with the week before my key race still over 100 km in volume.