I think I do quite well. I also have a successful background running and coaching. First hand with a 1:44 athlete during one point of his career along with other sub 4 athletes. Periodization training (strength/aerobic)/coming off cc, etc. Obviously his 12.5 is an very rough estimation. Everyone is different though. Nick Symmonds, who know is still is overall great physical fitness, just struggled to run a 1:59 and a 55. This is a guy for example who ran ~just under 1:17 at Millrose as well in 2013. Remember what he did at world's that summer? 1:43.55 and almost won the entire thing. You take Nick out of a cross country season and run in him a flat 100m and compare it to when he's in peak track shape, it's night and day. Enough said. I'll love to continue more convo if you care to learn.