Well, some of this is of questionable validity, because I tweaked my knee a month ago. This may have been a one-off chance of happenstance (the same thing happened to Jason, a veteran runner), but it may be due to my 'breakthroughs', in which case they're more like 'brake-throws,' as in throwing the brakes on my running.
1.) Variation. Realizing I don't have to run the same, steady pace all the time. I can vary my paces and ranges of motion. This makes recreational running much more recreational for me. I can even sprint if I want to, dammit, despite being middle-aged.
2.) Speed. It's better to run faster than farther (for me). I would rather run three miles at 8mm pace than 10 miles at 10mm pace (although the two are by no means mutually exclusive). I used to think serious running was all about mileage, but I just don't enjoy the plodding feeling of running slower. So better to learn how to run fast first and then add distance, just as the Kenyans do (although their fast and distance are quite different from mine, obviously).
3.) Gadget. I like having a running gadget. I bought a Garmin in June. I like using it on new routes and for checking my pacing progress, but I also like running without it and not thinking about pace at all, like in the old days (before June).
4.) Zoning Out. There is no number four.
5.) Gravel. Yes, I can run on gnarly, backwoods gravel, just like Ken Bob says you can. But no, I don't want to. 13+ mm pace is not my idea of a good time. Although I like the pure barefoot challenge of running on gravel, it hardly feels satisfying qua run. The sandy gravel of the nearby HS track, on the other hand, is an abrasive blast--gritty soleful pleasure at its best. Still, nice to know hardcore gravel running is possible in case I need to make a beer run or run from a bear while camping.
6.) Jewelry. I look good with toe rings. My wife has a gold band representing her on my ring finger, so I figured my kids deserve some silver bands on my toes. I like the incongruity of wearing them on my otherwise unadorned, straight-out-of-the-box body. G.I. Hippie.
4.) Trails. Opps, I guess there is a number four: one can run on trails. I used to think they were just for hiking, until I started reading BRU. Too bad the nearest trail is a 25-to-30-minute schlep away. Ignorance was bliss, now I feel deprived.
7.) Gravity. Are we allowed seven breakthroughs? If so, I learned that gravity can do all the work for you. I tried this once, but I didn't get a workout, so I went back to using my body. But seriously, it's been helpful, if not necessarily a breakthrough, to learn how to distinguish the useful ideas floating around BFR circles from the wacky quackery.
8.) Massage. Opps, I almost forgot. I discovered the importance of massaging, especially my shin muscles. I spent over a year with on-and-off-again top-of-the-foot-pain until I re-read Jimmy Hart's article on it and got clued in to 'referred pain' and how the tendons in the foot are connected to the muscles in the lower leg. I wish this breakthrough would've come a lot sooner. I would've made a lot more progress during my first year back into BFR if I had, and maybe would have even more breakthroughs to report by now. I guess this was probably the real number four on my list of breakthroughs. Actually, it's probably number one. Have the email notifications gone out yet?