Every now and then, I am asked to sign an NDA before reviewing some of the initial details of a startup that has reached out to me.

Like an angel investor or VC, I do not sign NDAs to discuss your startup.

Here's a quick summary of why I stick to this:

Ideas aren't unique; execution is. My focus will be on the 10,000 decisions required for execution, not just the initial idea.
Avoids conflicts. I meet with many founders, and I may have already heard similar ideas (or will hear them in the future). Signing an NDA creates unnecessary legal risk that I might be accused of sharing information, even if I haven't.
Reduces friction. It eliminates paperwork and administrative friction that slows down initial discovery.
Filters for quality. It helps filter for founders who understand that the primary value is in execution and who are coachable.

That said, I do, of course, always act in a professional manner, treat the information I review as strictly confidential, and use it only in the best interests of the company and founders, even without a formal NDA in place.

Of course, my formal engagement contract includes a confidentiality clause, since we're dealing with very important lower-level details.