Validation
You know the situation: You've written a great new product, you've just released it (much to your own relief, everything seems to be working) and now you're contemplating the next steps.
A little while later, you've done your homework, you have a Facebook page, you have a Twitter account, you have put your release out there on Reddit and Hacker News and StumbleUpon and even Delicious. And somehow, nothing happened. Maybe you've sold a copy or two, but annoyingly, the masses don't seem to be noticing your nice little App at all.
At first, your spirits don't mind. These people, they'll come! They'll find my pages, they'll notice my marketing and see my ads. Maybe after the next version? Maybe if you tweak your analytics just a little bit more...
Some days pass, and nothing happens. Your spirits really do start to mind, and indeed they fall at the same rate that your helplessness rises. You sit around sulking and think about what you did wrong.
And all of a sudden, this happens:
At that moment, you know what's missing: Validation! You needed someone to tell you that some of your stuff is interesting. That at least someone is looking at it.
Now, you can continue!