Realizing that I had gaps, identifying them, followed by addressing them.
I trained with a group of powerlifters that had been mentored by guys like Larry Pacifico and Don Reinhoudt. Jeff was the elder statesman of the group and was very good to me, he was a smart man and lifter. We were talking on one occasion and I was lamenting how I was slowing in my progress. He was straight with me and told me that in his opinion I had weak hips.
What?
But I'm squatting and deadlifting, etc. He suggested some things that really helped. Now the rub was that because of people's schedules my training partner was Mark Chaillet. Mark was on his way to being a major force in powerlifting and I was a tall guy with no particular gifts. The other guys were "supplementing" and I simply wouldn't do so. Since I was relatively strong as compared to the general population I soldiered on doing the basic routines of the other guys only lighter, much lighter. Had I taken time to ponder my gaps I would have been much better off, but this was the 70's and the science wasn't there. 3's and 5's made you stronger, that much I knew.
I tried to apply looking for gaps from then on. Dan John's work has helped. What difference it would have made back then I'll never know, I'm thankful that I didn't hurt myself.