Problems are relative, whether you've lost your keys or you're starving in Africa, stuff that happens to you are measured on a scale of your previous experiences.
A guy says "Rain AGAIN! I swear to God if I can't go body boarding this week, I'M GOING TO FLIP OUT!", in that moment, the world is out to get him, and the world is a terrible place. But then something in his brain goes; "What are you on about?? Are you really whining about this??" and the guy slowly gets over it. While this is happening, someone else, in another part of the world, is just happy that the water they just drank only had one kind of parasite in it. We measure our life to a certain standard, and we certainly notice when it falls below it.
This is where we enter dangerous territory, we have a serious thing to be bothered about, and it's generally accepted that we're not going to be ok with it. But this means we don't have anything to pull us out of it, we have an excuse.
See if you can remember some things you were mad about before your injury, there must have been one occasion. I'm willing to bet they seem trivial now! But the point is that at the time, they seemed awful.
I don't know how far along you are in terms of when your brain injury was, but it's been 16 months since mine. I'm going to assume that my surgery is working, and I'm working extremely hard to get what I deserve; that being everything I used to have. I've been doing my degree, I've been running, I've been doing weights, and I'm continuing to learn the piano. I sleep like an absolute dream at 10pm and wake up at 8am, that kind of clockwork keeps me motivated and keeps me supplied for the next day.
The brain is a miracle, and is surprisingly capable of adapting and improving. We have to work for it though, it's tough luck, but that's the way it is. It's quite literally a case of use it or lose it.
We might feel like crap going out there and getting on with it, but we have to get our bodies to man up, so we can drag it out of the house and get on with the things we want to do.
DO YOU FEEL IT?? That, m'dear, is the feeling of progress.