Often I find myself in a creative block simply due to thinking about myself "being in a creative block". Whatever reason that got me there in the first place (not finding the right word, spiraling digression, etc) no longer matters. Now, all that's preventing me from writing is just thinking about the fact that I am unable to write.
In fact, this paradoxical effect of self-awareness is so prevalent in creative endeavors.
This is especially true to art forms like poetry. Thinking about writing a poem whilst writing it is almost impossible. You inescapably fall into the trap of judging your poem before you even write it. You begin thinking about the other poems you've read ("am I sounding too much like Ginsberg?"). Then, once you begin deliberately trying not to be influenced by other writers, you find yourself unable to write a single word.
Part of the reason, I believe, is that when you analyze the emotions behind your art, you can no longer experience and therefore express those emotions fully. Somehow, the act has become too rational, too structured. You stop trying to paint the inexplicable, and start trying to make sense of it. But that's the business of writing essay, not writing poetry.
This is why I suggest anyone aspiring to become a creative writer not to major in English. Four years of Literature classes will force you to develop the habit of analyzing everything you read, which in turn will destroy your ability to create. For a reader, that's ok, but for an artist, it is a death sentence.
Of course, other art forms like story-telling and film sometimes involve more deliberate thinking. However, the same paradox applies.
Too often a very good short-story writer fails to start a novel because she cannot stop thinking about the fact that she is writing a novel and not a short-story. Some of it, no doubt, is the anxiety from the self-fulfilling fear about losing one's ability to create. Some other part of it, I believe, comes from knowing too much about one's own creative effort to allow the mind any breathing room to actually create.
There is something strange about the creative brilliance: It disappears as soon as you try to control it.
"Don't try," said Bukowski. I now think he was on to something.