I've heard before that you get the same kind of dopamine hit from saying you're going to do something that you do from actually accomplishing a goal. And that definitely seems in line with this behaviour I've noticed in people.
I personally try to not announce any grand plans I have to anyone. Maybe that's just out of fear of commitment, but I find the idea of announcing something and then having nothing to show embarrassing. But sometimes I do execute on my plans, and it feels good having the results to show.