I agree with the advice above. I've also noticed a couple things about the process of learning GTD that might help you deal. I have to go back to them all the time.

1. GTD is a martial art for the mind. You don't learn it overnight, in one week, one month, or even one year. But you get better at it and make it your own over time. For example, I still struggle with renaming my contexts to something that works better for me, and I've been practicing GTD for almost a year now. I'm still not a GTD ninja, but I'm much further along than when I started.

2. You will keep finding your weaknesses. They'll be there despite your best intentions. For me, I ignored the weekly review for a long time and finally it clicked for me. You turn a weakness into a strength and move on to the next weakness.

3. Be realistic about putting things on "hold" or "someday/maybe." I've started to put things there if I won't get to them this week. Otherwise the list is just too huge and it gets depressing. If I can't do it this week because it's not that important, it goes on hold.

4. Do a "mental dump" or a review whenever you feel anxious about all the stuff you have to do. It satisfies the paranoid part of your brain that doesn't trust the system yet. And you won't trust it until you know you will review it.

5. Keep it enjoyable. If you like index cards, cool. I can't stand the things, so I use OmniFocus. If I had to use paper I'd scream and never make it. I have to be digital. Some people have to be analog. Whatever works for you, that's your flavor of GTD. Like Merlin says, use a tool you like to use but not too much. If you don't like it, you won't use it. If you like it too much, you'll waste time playing with the tool itself. Just don't force yourself into someone else's flavor because you think it's gospel. When I teach music to a student, I always keep it fun or they'll give up. Same thing here. Enjoy the process.