An oldie, but worthy of a link: http://blogs.plos.org/neurotribes/2011/10/05/whats-the-most-important-lesson-you-learned-from-a-teacher/
I have since tried to identify a specific teacher and lesson for my own story, but I am not good at recalling memories, and my university teachers were pretty old school, sage-on-the-stage types of teachers, not exactly my style.
The one person that keeps coming up is my first kayak instructor (name forgotten) when I was 16 (?), in France. It was just me and him, and he really focused on breaking kayaking down the basics: reading the water (currents and countercurrents) and weight position in the boat (left-right and front-back), followed by exercises that internalized those basics before moving to the next step. With this as a foundation, I was ready to confidently tackle more challenging rivers in completely different situations, independently in later years.
Sounds like a life lesson for me as a teacher.