[alexandros]

The problem is that the engineer's "I don't know" gets beaten out of you when you speak to users and investors. You get made to feel like an amateur for admitting uncertainty. Which is absurd in the startup world of all places. So it's one of those doublethink situations, where you need to keep your internal accounting separate from the marketing talk. And then you need to know who to tell what on top of that. And then actually deal with the actual uncertainty on top of that. As if startups weren't hard enough in general, we're making it even worse for ourselves.

[dredmorbius]

Those are probably users and/or investors you're better off not having. Conversely, answering "we're not sure, but here are some parameters of the situation / dimensions" suggests you're at least cognizant of the area.

There's also the case of implausible ignorance: the "I don't recall" defense popular in politics and business PR-speak. This tends to decrease credibility.

[dsri]

A lot of people have the situational acumen to know when seeming to admit flat ignorance is a bad idea.

If you're not sure about a particular fact, make an educated guess if you can or relate what you can from memory, and say, "I'll have to check on that and get back to you," then actually check on it and get back to your questioner or the audience later.

[vacri]

When I worked as a hospital tech, I was the 'user' of a few sales reps. My favourite sales rep was the guy who would say "I don't know" or "I can't tell you", and jot down the question in his notebook to find out and return with. He didn't always return (can't have everything, I guess), but "I don't know but will find out for you" was far superior to me as a user than the usual sales misdirection or bullshit.

It really depends on who your users are, I guess. The general public aren't particularly grateful as a whole, but niche users tend to be more understanding.