I've though about this a lot over the last 30 years of cooking steaks. I learned to cook a steak this way at an early age. I now go up to 3 flips depending on how well cooked they want their meat.

It was cooking the humble chicken breast that really enlightened me as to the why behind this superstition. I cook a very juicy chicken breast by the way. The trick is to not overcook it.

It's really to do with knowing how cooked the meat is. Once you turn a steak, you lose most visual cues that signal how far the heat has penetrated your meat.

This can be easily overcome with a meat thermometer.