This happens to me all the time. I announce that I'm going to do something — take more photographs, write an essay, take guitar lessons — and after telling a million people I'm going to do it, I let it fizzle.
What gives? This interesting essay suggests that one reason is that when you announce your goal, you're making an "identity goal," or announcing an intention to "commit to an identity," — in my case, Photographer, Essayist, or Guitar Player.
For some reason the pressure is on, then, to be that identity, and you're less likely to follow through. In an experiment, researchers who published their findings in Psychological Science had students who wanted to be psychologists write down two things that week they were going to do to commit to that goal. They were told someone would follow up with them later to see how they did.
The catch? Half of the students were told, after they wrote down what actions they would take, that no one would actually look at their list or follow up with them. The fascinating conclusion to their research: the students who thought no one would follow up actually spent more time working on their goal than the students who knew someone would check on them.
So now I will run off and work on something — I just can't tell you what it is.