Lynne Truss discusses the helpful nature of friends' input into your creativity:
All writers learn this, in time: don’t show your work to other people until it’s safely finished. Even discussing your unborn book in quite general terms can be such an undermining experience that, afterwards, you give it up and go to live in Guatemala. “While I support you in your endeavour totally, I also think you should stop this madness right now,” is the nub of your friends’ response.
Personally, I haven't noticed this undermining of my ideas (possibly because my sheer egotism pushes through any arguments from the poor souls who let me hang out with them). Instead, I find that if I share some brilliant new idea for a story with someone, the dam is burst; the idea is (roughly) conceived and set free in someone else's brain, and I'm usually done with it. This is most likely one of numerous character flaws.
I expect there are many marvellous counter-examples in history of writers and artists receiving proper help and encouragement from their friends and acquaintances. I expect that T.S Eliot, for example, never regretted the day he asked Ezra Pound to give The Waste Land a bit of a professional once-over. But generally, the wisest course is never to describe the work one is doing.
Lynne also posits an entertaining discussion between Leonardo da Vinci and his mother, about his idea to paint the Mona Lisa.