Here's my experience. Trained hard, off and on, 1998-2001. Graduated, took a demanding job, and didn't train again until 2011. Eating crap, drinking every weekend -- total disregard for my health
What lit a fire under my butt?
Really awful health markers (BP 149/89, weight 263 lbs, height 6', blood sugar "pre-diabetic") and a 3 year old daughter.
One morning I woke up and had a strange thought -- would I rather have a successful career and be dead soon, or be a total failure with my career and healthy/active for the rest of my life (and hopefully do some really cool stuff with my daughter -- ski, hike, bike, swim, surf, camp, etc.) There really was no choice.
The reality is somewhere in between (career success and health).