Being asked to sign an NDA for more than a few times while assisting early stage startups in their projects, I thought to make my life easier. Here’s my polite reply to such inquiries:
I’m happy to discuss with you about various aspects of your project! However I consider carefully when writing an NDA, and the answer to writing one is probably “no” - here’s why.
Writing an NDA with a non-proven business is risky for me. You are free to let the idea down, but I have to oblige the NDA for a specified period of time.
While working on early-phase concepts, pivots are common. Ideas cross-breed, but with signed NDA, I must now avoid ideas from certain areas. This naturally limits my productivity in all of my other projects.
Since I expect agreements to be mutually beneficial, I assume something in exchange for writing an NDA. This something can be for example money, or a fair contract for billable work.
With so many ideas floating around, I certainly have my own list of ideas. Those ideas are such that I already see them having potential. If I would like your idea, it would be one of the many ideas that I like.
I also know that the execution is what matters, and I would probably need you (and one of your essential skills) to execute on the idea. Therefore, you can feel safe that your idea is not stolen.