I don't think his comments translate into "you are stupid." They translate very clearly into "that is a terrible idea." With perhaps a shade of "don't 'pivot' because your feet are cold."
Which is super-valuable guidance!
That's not to say it's pleasant. Clearly communicating that you think someone is making a mistake often sounds like a personal attack. (Maybe that is a personal attack, at least if your decision-making process is deeply intertwined with your identity).
But in person, without preparation, in a few-minutes-long meeting? You're going to hurt someone's feelings. Guaranteed. Just think about how long it would take you to "correct" someone in an email, communicating that they are totally wrong, but not hurting their feelings at all? Heck, we probably each spent about as much time writing these comments as the interview took in its entirety.
There is one personal rule that I feel strongly about, though: never say anything negative in public (or to colleagues) about someone that you haven't already leveled with them about, and ideally given them a chance to change. I don't know if pg did that with the thermostat startup he trashed on Twitter recently, although it's not really any of my business.
It takes time to develop good judgement. Many ideas that seem initially appealing turn out to be tarpits that ensnare founder after founder. And some ideas that seem crazy at first are actually good. And many ideas are bad initially, but "ripen" as technology changes.
For example, WebVan was a huge failure 12 years ago. But today Instacart is providing a very similar service, but in today's context they can do it without burning tons of capital.
Part of the benefit of YC is that they see so many startups that they can develop keen intuition into which ideas are most likely to work. Not perfect intuition. But definitely better than the average first-time founder.
Consider this: If some random person after listening to you presenting your idea says a. "that is a terrible idea" or b. "you are fucking stupid." Does it matter? B may be more unpleasant to you, but both A and B express the exact same opinion about your idea.
Anyway, I think you missed my point. Nobody cares if feelings get hurt, but expressions like "like moths for bad ideas" aren't brutal honesty.
What would Spock have done when brandonb and his partner presented their (supposedly well-researched) idea bout changing the company? He would have said "My instinct tells me that your idea is detrimental to your business. But this meeting is to short for me to analyze all the facts and formulate a final opinion. Please get back to me next week and I will explain what I think the major weaknesses of your business plan is."
That would have been unfiltered and brutally honest. But it is also possible that it wouldn't have persuaded brandonb to change his mind.
I agree with you about people using Steve Jobs-esque "emotional towel-snaps", and how reactions to them may thus be emotional and not rational. Check.
I'm saying, though, that if you clearly (and quickly! within minutes or seconds!) communicate 'you came here for my view, and it's that you're wrong. don't do that', people will read that as emotional, maybe as 'mean', regardless of whether there's any explicit emotional content there. No one likes to hear that answer, so their distaste at getting an answer they don't like makes them view it as an attack.
But I don't see that anything in pg's cited words demands a translation to "you are effing stupid!" It's reasonable for an adult who is basically paying equity to get actionable advice from a trusted investor not to interpret said advice as a personal attack.
To illustrate my point: your 'Spock' answer assumes a much friendlier reality than pg may have seen for them.
What if 'Spock' is convinced they were having a hard time buckling down, that if they changed focus that late in the game, they'd have died?
Then he would have essentially paraphrased pg's response: 'I am as sure as I can be that that is, qualitatively, a terrible course of action. You've nearly died already [moths for bad ideas], and I'm sure you will be dead if you do this. My time's up, so let me know what you decide next week.'