Popularisation, extremely short
When intentions go public: does social reality widen the intention-behavior gap?
Source
New York University, Psychology Department, New York, NY 10003, USA. peter.gollwitzer@nyu.edu
Abstract
Based on Lewinian goal theory in general and self-completion theory in particular, four experiments examined the implications of other people taking notice of one's identity-related behavioral intentions (e.g., the intention to read law periodicals regularly to reach the identity goal of becoming a lawyer). Identity-related behavioral intentions that had been noticed by other people were translated into action less intensively than those that had been ignored (Studies 1-3). This effect was evident in the field (persistent striving over 1 week's time; Study 1) and in the laboratory (jumping on opportunities to act; Studies 2 and 3), and it held among participants with strong but not weak commitment to the identity goal (Study 3). Study 4 showed, in addition, that when other people take notice of an individual's identity-related behavioral intention, this gives the individual a premature sense of possessing the aspired-to identity.
If you have tags to suggest please do and I'll edit them in.
I suspect that it's not the telling of the goal, but the feedback you get from your audience that changes your ability to put effort towards a goal.
Dopamine drives action and is highest when the desired outcome is most uncertain (probability ~0.5). IE, If you're uncertain of success, but think it's attainable this is when you're most motivated to work hard. Therefore, presumably a goal that someone is already working hard towards already has a perceived probability of success around 0.5.
If your interaction with others about your intentions raises your perceived probability of success, through say comments such as "that will be so easy for you, you'll do great" this will lower dopamine. Conversely, if people say "that's truly impossible- you're wasting your time" and you believe them, that will also lower dopamine and reduce effort.
If you want to help someone achieve their goals when they explain them, the best reaction is probably to help maintain their uncertainty of success or failure. For example "that will be really difficult, but I think you have a chance if you really work hard at it" is probably more helpful than "you're so smart, I have zero doubt that you'll achieve the goal."
If you're already working hard on a goal, it's probably better not to confide in others because you don't know how they will respond, and how that might influence your ability to remain motivated. If you do confide in someone who is usually encouraging, it wouldn't hurt to explain a real reason why the goal will be very difficult for you to achieve. I don't know why you'd confide in people who are usually discouraging...