I recently read a story attributed to the book Art & Fear by David Bayles and Ted Orland. It recounts an experiment by a ceramics teacher, who divided his class into two groups. The first group was to be graded on quantity. They were to focus on making as many pots as possible by the final day of class. The second group was to be graded on quality. They only had to make one pot, so they could pour all their time and focus and energy into this one pot--but yes, it had to be of utmost quality to get an "A."
Now, my first thought upon reading this was to think, Well, of course, the students focusing on quality are going to have the better pots. They get to spend the entirety of their class time getting their one pot just right. But the curious thing is that by the end of the class, the students focusing on quantity were actually the ones producing the pots of the best quality. It turns out that even though they were focused on making as many pots as possible, these students couldn't help but learn from the process of doing so. They had the benefit of making mistakes and learning from trial and error. In the end, this was enough to put them ahead of the group focused on quality.
As writers, we face the equivalent of a lot of lousy pots. How many times do you end up tossing paragraphs, pages, chapters, or even entire manuscripts that just aren't making the grade? But the simple fact that we're writing means we're learning and honing our skills. Quantity leads to quality, which is why we must write, write, write.
So . . . go, write, fail! Fail a lot if that's what it takes. There is great value in mistakes. The most important thing is to keep writing.