There are a million reasons why it is important to talk to people about your new business and there are maybe three or four reasons to keep your new project a secret. The biggest reason to keep your mouth shut would have to be paranoia, by a wide margin.
Think of it this way.
Raise your hand if you know of anyone that has had their idea stolen from them directly. So basically, they were networking, told someone their idea and the person they told took the idea, started the company and became successful. Not only that, the success of the thief’s company is the reason that the original company failed.
Do you know anyone that could tell this story?
On the other hand have you ever met the guy that had an idea but only told a few people? The idea was so brilliant that it would obviously be stolen and all would be lost. Somewhere along the line things went wrong. He never told anyone, never generated any buzz or momentum and the business never launched.
Of course we aren’t talking trade secrets we’re talking business ideas, and ones that aren’t glaringly obvious. If you look at things logically, not talking about your idea is probably the same as not launching.