TL;DR: Requiring someone to sign an NDA just to hear your idea is unreasonable.
Every so often, I get an e-mail asking me for feedback on an idea, with a generic NDA attached that I'm asked to sign before I can hear what the idea is... I won't do that. And I'll let others much more experienced than I am explain why:
(The short version of each these is basically: "I can't and won't sign an NDA to hear your pitch or see your business plan.")
- Joel Spolsky (May 2000)
- Ramit Sethi (Oct 2005)
- Brad Feld (Feb 2006)
- Fred Wilson (Feb 2006)
- Mixergy (June 2009)
- Chris Dixon (August 2009)
- Anil Dash (May 2010)
- Stack Exchange (Jan 2011)
- David Freedman (Feb 2011)
- Alana Horowitz (Feb 2011)
- John Larson (Apr 2012)
- Carol Roth (Oct 2012)
- Carl Erickson (Sep 2014)
I’m happy to give feedback (who knows if it’ll even be useful to you), however the points in Carol Roth's article summarize the theme very well:
- Your idea already exists (or being new can be a problem)
- The value is not in the idea
- Sharing ideas makes them better
If you’re going to share anything generally considered “secret sauce” (like access to your code repository or the special formula for the Red Bull competitor you’re starting), asking for an NDA is a reasonable request -- you have to protect your property (however, a first e-mail typically wouldn’t be the place to discuss sharing that level of detail though).
If you're just sharing the high level idea, see it for what it is: something that hasn’t materialized yet and will likely change a lot as you work more on it.