I started twice daily workouts when I was 18 years old. This was nothing exceptional— everyone ran like an unchained demon back then. This was the Walker Dixon Quax era in Auckland, New Zealand, the stronghold of Lydiard territory, and everyone ran twice a day, even many recreational runners. My reason for training twice a day was simply because everyone else was doing it.
Thus, I assumed it was worthwhile and that it would payoff. Today, you’ll be hard pressed to find a world-class runner who does not run twice a day. This has become standard practice for elite runners for about 40 years.

Back in the prehistoric dawn of distance running, that is in the 1960s and 1970s, we had absolutely no understanding of the importance of sports nutrition for recovery and performance enhancement.
In the absence of any sports nutrition knowledge, all sorts of myth and superstition dictated what we ate to prepare for races, and we never put any thought into what we should eat to properly recover after running.