Besides the points already made by other such as LBYM early in career, like-minded wife, and good education, one decision we made greatly paved the way to ER:
When we met & got married we were both in established engineering careers. We knew we wanted children but weren't sure if both of us would continue working so made the decision to gear our lifestyle to live on only one income in case that is what we decide once children came. Once son #1 came, we had about three years of my salary saved up way more than enough to cover the cost of a custom built home for the growing family. No mortgage payments hanging over the monthly budget. DW became a stay at home mom. Four years later, due to organizational downsizing, was offered the opportunity to retire early at age 50. The decision to live off of one income for several years put us so far ahead financially that it enabled me to join her as a stay at home parent with minimal reservations.
No regrets, boys are now 17 and 15 and I've participated in their lifes constantly.