If you don't have goals you can quit either. I know this might be quite controversial. But I'm honestly suggesting yo stop setting those goals. At least if you are like me. For others, clear goals work better.
I remember when I was reaching both three year mark and a thousand post I was thinking of quiting. Maybe not seriously, but still the thought of quiting crossed my mind every now and then. Even if I never set neither of those achievements as my goals they still felt like ones. It was something to look forward. And something to fail on. Another though that was the "what next". Where would I focus after reaching those "goals".
It has been couple of months now after the three year mark. And I don't remember thinking about quiting once after that. I haven't had any new goals in sight, so I haven't had a reason to think about quiting either. It hasn't been an option because there was nothing to quit.
Setting goals make it possible to quit and fail in reaching that goal. All you need are purpose, direction and habit. With those you can reach as far as you want.