I was a 2:27 marathoner that seemed to have hit the ceiling. It seemed that I couldn't break that time. I ran a 2:20 marathon this past fall and a big reason for that success was due to coaching and guidance. Coaching is like having a second set of eyes on a problem.
As an active duty service member we are taught "Attention to Detail." I was focusing on my stronger attributes while neglecting my weaker ones. My personal coach pointed a few things out and changed a few of my workouts and like magic; I smashed my PR in the marathon.