Although I don't know the exact number of writers--or even an approximation--from personal experience I can tell you that sometimes I lack motivation to work on my current project.
I know that lots of writers will tell you that they "have" to write. Many fill their "extra" time with writing and writing related activities. To be honest, that concept is foreign to me. I write because I love it, because it's a wonderful way to create, but I've never seen it as something I "have" to do. Perhaps it is because I don't work outside the home, so that I am in the rather envious position of being able to write most any time I want. Thus, I haven't experienced the pressure of not having the time to write.
During the last several months, I've gotten myself involved in more writing related activities. I have this blog, I have joined a lot of social networking groups, I've guest blogged, and am looking at joining a couple of somewhat local writer's groups. I also have several books in various stages of completion.
To me, just doing these things can cause me to overload, and rather than rising to the occasion, I start to shut down, and even the easiest of tasks becomes monumental. Any motivation I had to write or create or work on my social networking falls to the wayside.
What is one to do? Many folks suggest taking a break from writing the current piece, and working on something else, something different. Perhaps another book, perhaps some editing, and so forth. I've done that, and still found myself coming up short.
So what I've done is learned to schedule things, to become more organized. Each thing in its place, so to speak. To keep ahead of the ball. Like with my blog, which involves posting ahead of time, and scheduling the post to be released on a certain day. I also work on writing things that don't have even a hint of a deadline. I go and clean the kitchen! I take time off to read. To visit with a friend.
What it all boils down to is taking time to renew and refresh--for me that means spending time away from writing. I get involved in some school activity that my daughter is involved in. I get involved in some physical activity; don't underestimate the power of those endorphins!
It may take a couple hours, a day or two. Perhaps a week or a month. But be sure to take the time to get away, to detox, until you know within yourself that you're ready to tackle all those things that you love and that make life worthwhile.