I think the biggest game changer for me was the idea that meaning comes responsibility. That brought me out of a long and dark time in my life when everything I thought I was and was going to be had been ripped away. I no longer thought I had a purpose or meaning. This idea restored meaning to my life, and has kept me moving forward since; it has provided a center.
For training, the biggest game changer was when I left barbells and powerlifting and learned that there was a way to train that allowed me to get up and down off the ground without having to brace myself for the pain. Leaving barbells for a time may have left me weaker at barbells, but it has drastically improved my quality of life. Strength and fitness can be built in many ways, and finding a way that doesn't hurt is not only possible but recommended.