First things first, are you wondering what an NDA is? If not, skip to the next paragraph. An NDA is a non-disclosure agreement. They're used in situations where someone is trying to protect proprietary information they're going to disclose to a third party (in this case, me) to keep said third party (again, me) from discussing that information with someone else.
Seems reasonable, right? You have this great idea, maybe you know me only by reputation, so you want to protect your idea before you give me all the details. Fair enough, but I won't sign it (most likely).
The first reason I won't sign your NDA is that it would significantly inhibit my ability to do my job. I get pitched at least once a week either as a vendor, a potential investor, or sometimes just as a sounding board. Your NDA would not only limit who I'm able to talk to about new ventures, it would also inhibit my ability to do business with my existing clients. We work with a lot of clients, SOMEBODY is bound to fall under the umbrella of your NDA.
Second, your idea isn't new. I know you think it is, but it isn't. At least one other person somewhere has had the exact same idea, if not something extremely similar, I promise. Just because you don't see it on the market doesn't mean nobody else has thought of it, is working on it, or has tried to build it. There's a saying I use often when discussing this concept. It's been said a few different ways but my favorite version comes from Gary Vaynerchuk: "Ideas are shit, execution is everything."
It couldn't be more true. I get pitched a lot of ideas, and you'd be surprised how often two different people think they have this amazing, unbelievable idea they can't believe nobody else has thought of - and they're exactly the same idea. Facebook didn't invent social media, Zuckerberg just executed it better. Instagram didn't invent photo sharing; in fact, the app started as a location-based app named "Burbn" - but Systrom and Krieger pivoted and executed. Then, in the same market space about a year later, two guys named Spiegel and Murphy came along and executed as well, and SnapChat entered the unicorn club.
Building on that concept, I have no desire to steal your idea. I don't have enough time to work on 99% of my own ideas, I'm certainly not going to spend it stealing yours. On top of that, if I was in the business of stealing ideas from friends, clients, or anybody else for that matter, the flow of those prospects would dry up pretty quickly.
Third, I won't sign your NDA (and to be quite frank, I'm offended when you ask) because you're flat out telling me you don't trust me before we even get to know each other. You approached me, I happily offered up my time (which I value dearly), and the first thing you do is tell me you don't trust me enough not to steal your idea. That's not really the best way to start off a new relationship of any sort.
My goal is to help you build and grow your business. If you don't trust me at the very least not to steal your idea or do something that would harm your business prospects, you shouldn't share them with me in the first place.
Finally, most NDAs are way too vague, so if you really want somebody to sign one, you better figure out exactly what you need to protect and write the NDA in a way that covers only that which is necessary. This represents the only situation where I might sign one. If you present your idea to me and the execution of that idea involves some incredibly important proprietary information or trade secret that would absolutely negatively affect the business if it got out, I would likely sign an NDA that specifically covered that information and nothing more.
The bottom line is that I'm not saying your idea isn't valuable, that it has no merit, or that you're not going to build an incredible business. What I am saying is that the idea alone is worthless if you can't execute it and I have nothing to gain from trying to steal it.
So the next time you pitch a vendor, a friend, an investor, or anybody else whose help you're asking for, ditch the NDA and focus instead on establishing trust and a mutually beneficial partnership.