Writers want their work to be the best it can be. This often poses a problem when it comes to maintaining good writing habits (which includes writing every day, or almost every day). No one is at their best every single day. Life and emotions intrude, and a writer caught unaware can find themselves churning out utter dreck in the name of getting words down on the page. So, if you're having one of those days, is it better to write crap - or nothing at all?
While no one method works for every writer, there are very few exceptions to the general rule that writing crap is better. It has been said, and rightly so, that great writing is not written - it's rewritten. For most writers, shitty first drafts are a way of life. To paraphrase Nora Roberts, one of the most prolific and talented writers of our time: you can fix bad writing, but you can't fix a blank page.
In my opinion, not writing anything when you aren't feeling your best is more harmful than churning out crap. It may be just me, but I feel lowest when I'm not producing anything at all. Even better, I can often start out writing utter dreck, and once my mood is slightly elevated by the appearance of actual new pages, I find that the quality of my words improves. It's the same principle behind the idea of faking happiness: act like you're happy, and eventually you actually will feel better.
So go ahead - write crap like it's going out of style. (And if you had any doubts that I'm actually stuck in the problem I'm describing, please note my use of cliche and hear me say UGH.) Now, I'm off to take my own advice.