When you find something negative about what you're doing, or it simply disappoints you, or whatever else it might be, you end up projecting those feelings onto yourself. When the activity or community begins to frustrate you, you can either be frustrated with yourself or realize that you've grown beyond it.
Like Matt, I spent some time making a living at poker, and like Matt I have been a Hacker News member for over 3-1/2 years (I just realized that there is only one day separating our join dates). I feel like I have a pretty good idea where he is coming from. When you find that the quality of your life is being diminished by something you're doing, and you have the power to remove yourself from that activity, then it is time to do just that. I commend him for having the courage to do that.
I know people will complain about him leaving loudly. Personally, I have also tried to quit poker and Hacker News, and in times when I have a lack of direction, I find myself wandering back into old habits. Quitting loudly is a small measure to take to give people the chance to help you stick to your decision, to hold you accountable.
Good luck, Matt.