On the other hand, the number of pieces I have stated my intention to learn, and never done so, is far greater than the number of pieces I actually know. I think it's just so easy to say "I love this piece, I'm going to learn it." Well, that took 5 seconds to say, but it will take 100 hours to learn the piece.
So, for me, it comes down to how truly/deeply motivated I am to begin with. If it's something I truly want, announcing makes no difference. If it's something I'm lukewarm on, I'm probably likely to announce something impulsively and commit myself to something I didn't think through.