The hardest I find about breaking 80 is the "luck" part. There seems to always be a part of my game that's missing on any given day. Somtimes every 3-foot putt is an adventure, sometimes I can't miss a 10-footer if I try- but on that day I can't find a fairway. When I'm hitting it solid and straight off the tee, I'm thinning chips or struggling with wedge play around 100 yrds. It seems like it's a perpetual circle of play when every part of my golf game takes turns showing up.
As a 9.4 present handicapper, I've broken 80 about 10-15 times in my life, but that is still only a very small percentage, and I admit, I do play tougher courses with high ratings and slopes on weekends. I've hit low to mid-80's at times there, which would be high 70's at my home course. No matter how much I practice, 95% or so of every time I leave for the course, I will leave an important part of my game at home, and it really hinders my chances at a score in the 70s.

As a small shining star inside though, the feeling that I've done it before shows ability I have somewhere lurking in the depths of me.