Sales. You know, as probably every programmer out there you finish your product and you think that clients will start flocking in because you've build such a fucking great service. And then reality hits you in the face and you realize that the hard work just started. You have to go and talk face to face, listen to their needs, adjust your service accordingly, pamper them because they can't understand half of what you're saying, publish and then repeat.

The good thing is that once you get the grip of it you feel invincible. All the fear and the doubt you used to have while building a product disappear because now you know how to approach clients, and if you're smart enough you won't even start building a product without first having some feedback from potential clients.