Quake, or any FPS or any game, hell even LIFE is all mental. You being where you are is not because of limits, you're where you are at because of your mental game. People like to put limits on things when they really shouldn't. You also gotta dedicate yourself to this game to reach higher levels. I'm a rager, but now i'm choosing to stop playing that drag down mind game and start playing to get good at quake, or any FPS because games are more fun when you're dominating. Don't ever sell yourself short in video games, or in life. What's stopping you from reaching higher levels? you are. If you wanna play for fun, then play for fun. But if you're looking to become good, or even great? stop looking down on yourself, and do what you want to do.
http://www.youtube.com/watch?v=sqummot83IE
Someone on these forums gave me that video and it's really hit home with me. GREAT advice from a pro gamer (other games he played at a high level besides Street Fighter 2).