What is even more foolish, is to not even try to write because you are afraid of making a fool of yourself. Go and write!
There are times when we write that words flow through us like a river of creativity. There are other times where the words are the last bit of ketchup at the bottom of the bottle. You need to remember that, with enough patience, the ketchup will come out. So, if today is a day where you write a thousand words, or two, forward is forward!
Great writers know... You may not be a great writer yet, but as long as you keep moving toward your goal, you'll be successful eventually. Keep moving! Keep writing!
Do you think too much about what you're going to write? Wonder if an agent will like it? Or a publisher? Do you cross off ideas just because you think it won't sell? Don't waste valuable writing time by second-guessing your ideas and inspirations. Write what your heart is telling you to write.