Tests done since 1933 show that people who talk about their intentions are less likely to make them happen.
Let's suppose this is true.
Announcing your plans to others satisfies your self-identity just enough that you’re less motivated to do the hard work needed.
This does not follow. There is no evidence on which way causality runs. Maybe people who are more likely to succeed, and hence confident of success, don't bother to announce their plans.
A blog post by Derek Sivers links to evidence that stating one's goals makes one less likely to accomplish them.
Excerpt:
Link: Shut up! Announcing your plans makes you less motivated to accomplish them.