If you were the subject matter expert, and some guy appears and tells you that you're doing it all wrong, ego tends to play a bigger role!
For (2), yes. The 'it must be presented to me in a way that does not make me lose face' part still applies.
For (3), not really. My 'patient' has just died - I cannot hide from the fact that there is probably something better that I could have done - and the other (lay) person has more experience of this situation than me. I would not say 'hey, I've known farming for 10 years, I'm not going to listen to you'.
The situation is more about someone coming to you, a person who take care of your animals for 20 years now, saying that a particular fruit that just grow in mountains can save your animals when they eat before noon. And to support this he ponts out that his animals have much better survival rates.
Imagine that the reality is that just eating that fruit, grown wherever, any time of day, already improve your animals health.
Sure, the right thing to do is keep testing the different hypothesis until you understand why his animals have better health. But if the guy comes yelling at you, very arrogant and calling you ignorant and stupid; it might be just too natural to realize that fruits growing on mountains are the same that grows everywhere; so everything the guy says must be bullshit. F* that guy, who he think he is?
But the general response was not "well, that's a theory worth testing". It was "This guy is crazy. Gentlemen do not pass disease". I have read no record of an alternative theory of the high mortality rate that anyone else had advanced - one might have existed, and was lost in the myst of time. But I find it just as likely that there were, in fact, no competing theories.
I have unfortunately witnessed a modern day case applying to a much smaller population. Not much has changed. I know a doctor who has literally (and provably) saved at least ten lives based on his understanding of a disease, which he cannot support with statistics yet - his statistics keep improving with every case, but still not at the publishable 0.05 threshold. And this is an extremely rare disease (in the order of 1/1,000,000), so it might take 10 more years until he has a rigorous proof. (Alas, giving more details would basically be naming him and myself, which I do not wish to do)
His theory is a lot easier to accept than the prevailing theory about said disease, except that accepting it proves incompetence of many in the field, including editors of medical journals -- which, indeed, is the case, but those cases are dismissed as occasional random misses rather than the systemic incompetence that it is.
It is possible this doctor will retire before they have enough evidence to publish their results. And despite the amazing results so far, when I went for a second opinion after talking to this doctor, 4 others told me that he is making a mouse out of a molehill, and that it's almost impossible that he is right. Luckilly, imaging results proved he was right, and another life was saved. And you know what? Of those 4, only two realized they need some introspection, and the other two dismissed this as a "lucky guess".
The more things change, the more they stay the same.
P.S: Said doctor is extremely humble, and communicates very clearly.