Then there are the days when the words gallop into existence, as opposed to the days when the words trickle out in a crawl.
That, I suspect, is the difference between an amateur and a pro.
In the day job when the words are due, you just turn the spigot and out they flow. If you want to be a professional author, then author-type words need to flow when you turn the spigot.
A professional may write “when the mood strikes,” but he makes damn sure that the mood strikes when it’s time to get to work.
If your business is words, you need to ship words when you say you will.