[T]he first perfect nihilist . . . has even now lived through the whole of nihilism, to the end, leaving it behind, outside himself.
I am frequently gripped by the cosmic unimportance of my life. Most people would assume this sort of preoccupation necessarily precipitates an existential crisis. But at least in my experience, no particular kind of attitude seems to follow. I might be foundering in anguished catatonia; or soaring in exhilarated engagement, bounding from wonder into wonder. In fact, sometimes the very knowledge of this profound insignificance itself seems oddly exhilarating. (I'm weird that way.) The point is, if nothing matters, the the fact that nothing matters doesn't matter. So you might as well seize the day.
This is why the standard reaction to nihilism - that nihilism would leave anyone without any reason to do anything - is so deeply misbegotten. Why would anyone need an external inducement to engage in satisfying, fulfilling activity? Once posed, the question can be seen immediately as absurd. It reminds me of the perverse notion (often attributed to Dostoevsky) that without God everything is permitted. If it is only the threat of eternal torment in the Lake of Fire that keeps you continent in your impulses to crude, thuggish violence and debauchery, your problem probably isn't so much the absence of divine punishment as it is an absence of a decent-sized prefrontal cortex. Much the same goes with the relationship between reasons and self-realizing activity - if you find yourself unable to get excited about doing cool stuff, reasons aren't going to help; what you need is therapy.
The best way to overcome nihilism is to accept it. And leave it behind, outside yourself.
UPDATE: Aaron Weingott dissents.