These questions are somewhat rhetorical, but if you're looking for actual answers, I encourage you to check out this blog post. (The blog as a whole is actually pretty interesting.) More importantly, however: how can you (we) stop procrastinating?
Acknowledge that you're procrastinating. The first step, as they say, is admitting you have a problem. In all seriousness: if you don't recognize that you're putting off something that's important to you (in this case, writing), you can't stop procrastinating and start getting work done. We're all expert rationalizers and justifiers. If you direct your energy at explaining away your lack of progress rather than—well, progressing—you're never going to get that short story or novel written.
Try to identify the cause of your procrastination. Ideally, you'd rush home every day from work to sit down at your computer/desk/notebook/&c and start typing/scribbling away. If you aren't, try to figure out why. Does work drain too much of your energy? Are you stuck on a scene you're not having much fun writing? Is your writing space depressing, distracting, or (worse) non-existent? Once you know why you're having trouble putting pen to paper (or fingers to keyboard), you'll hopefully be able to overcome the problem.
Set small, manageable goals and stick to them. If your goal is 1,000 (or 100!) words a day, write 1,000 (or 100!) words a day. Period. No excuses, no rationalizing, no justifying. Caveats: emergencies arise. Family is more important than writing. Sometimes you're not going to get those 1,000 (or 100!) words written. What does that mean? It means that tomorrow, you write 1,000 (or 100!) words. Keep moving forward and don't look back.
Periodically reward yourself for sticking to your goals. Whether you do it by scene, chapter, or word count, reward yourself when you achieve a major or meaningful milestone. It needn't be anything big, but the prospect of getting or doing something you truly enjoy as a reward for maintaining your writing schedule can work wonders. There's absolutely no need to "punish" yourself when you fall short; you just won't get your chocolate/iTunes/True Blood/&c fix. (Make sure you pick something you really want.)
That's all I've got for you today, mes auteurs, but if you have any tips for defeating procrastination, don't hesitate to share them in the comments!