most of these guys have arthritis bro thats why! hahahahaRead the program in it's entirety and it should make sense. No offense if you ask that type of questions I can tell you haven't read it all or haven't read it closely.
Essentially -9 actually means "7-9"... Start with a weight where the last rep you can do is the 7th rep. Keep using that weight until you can get 9 reps. Then up the weight to bring your rep's back down to 7.
There is so much ridiculous weight training theories, ideas, programs, techniques etc out there.. And from the bottom of my soul, 98% of the ppl who pick up a dumbell need to ignore them and stick to the absolute basics. That program I gave you is the absolute basics with intelligent sciencfic reasosning behind it. Just stick to that program and follow it to a T.. Don't need to change a thing except swapping exercises once in awhile. But when you swap exercises it has to be the same type. So if your swap out flat bench because your stagnent on it, change it for an exercise that hits that part of your pec in the same way such and smith machine bench or dumbbell bench.
Other than that, diet diet diet diet diet.. Your diet needs to be tailored to you and your goals and it has to be done correctly and followed to a T.. getting a lifting program that works is fiarly straight forward, but making a diet is more difficult.. might be worth hiring soeone like funnyman to get you on the right path..
Other than that.. more I can tell you.. most people who are currently lifting are over trained lol.. spend a lot of time reading about over training, the signs, symptoms, how to avoid it and how to heal from it.. Over training is a son of a bitch that will stop your progress faster then a poor diet.
Laslty.. I'm not sure WTF is with guys who lift weights now anymore, but no one I see ever wants to do HEAVY sets to failure.. You want to know the most important rep ?? It's the last rep.. if your last rep of your working sets isn't the very last rep you got in your body, then your not going to progress.. It's crazy, but I've lifted with guys who say their working bench is like 200 for 6 reps.. but then we lift together and you teach them and show them how to push themselves and in the very same workout, they do 200 for 9 reps lol.. No one I see anymore knows how to push themselves to complete failure.. I know for me, I never grew or got stronger until I told myself every damn time I did a working set that its going to be to absolute failure or nothing.
I correct myslef lol.. I do see guys training to absolute failure on biceps and triceps lol.. that's it..
I will add from my last paragraph I exclude guys who are getting older.. when your older you need to train differently sometimes, not always to absolute failure..
Do yourself a favour and watch "blood and guts".. Dorian will show you what absolute failure and lifting heavy is all about.