Funny, I got the same advice sans drugs about NaNoWriMo a while back, and was just passing it on recently to someone else. The way it was put to me, though, was that "you can only tell your story once." Not literally, of course--you can relate what happens in it more than once--but you can only really tell it and put your heart into it once. Don't waste it talking to your friends about the idea. Get it on paper the way you feel it. Then tell your friends the lesser version afterwards, or just wait and let them read what you wrote down.