What is the Bigfoot? What is the Chupacabra? Do these exist? Many people have seen them throughout the years, and swore to the validity of their experiences. Of course, they experience something, but what they are experiencing may be something other than what they appear to be, and what people are experiencing probably vary widely in what they really are.
Ok, this is not a good metaphor, perhaps, but I would argue that what we call writer's block is no more real than any of these two mythical creatures. Of course "something" is there, something that prevents people from writing. However, I believe that writers block is probably really an easy catch word for a variety of biological, psychological, and social phenomenon that we lump together. The consequences of doing this area great- if you do not diagnose the actual nature of what keep you from writing, are not likely to find a good solution.
Here are a few of the possible phenomena that I have seen subsumed under the term writers block:
Poor writing habits
Environmental issues (i.e. a bad chair, too much noise)
A history of being judged for writing issues
Lack of good mentorship
And many more...
Your job is to understand the actual nature of the barriers that get in your way. To adopt a highly dubious social construction such as writer's block will keep you from making the changes you actually need to make to further your writing and publishing agenda.
This will not be the last time these issues are addressed.