Marriage creates a structured life outside of work that gives PhDs an anchor to return to periodically. This leads to better long term and consistent progress.
Stephen King describes his success in writing in part due to his successful marriage. There may be some similarities there.
His theory is that wife and kids out a gun to his head that he had to learn to swim and quick
At an old job (natl. lab) there was a guy who does his research job for, maybe, two or three hours a day. The rest of the day he is reading unrelated books.
But those three hours are so productive that by March he has filled his employer's scientific paper quota. His managers hate him because they see his fucking around 70% of the time, but by any performance metric (especially quality. His papers are the consequential ones)he's blowing everyone away.
Love my family. love wife and kid. Have never been less productive or efficient in my life.
As a stickler guy between 20 and 34? Relentless productivity, focus, and time.