The difference is whether the person is expected to manage the situation on their own. If I said that to a buddy of mine who I know works on his own car he would be upset. He imagines himself capable of working on cars and I just communicated I don't think he can handle it.

Nobody wants to be the person that other people see as a basket case. Just because someone is upset doesn't mean they can't solve the problem.

You can make a scenario where anything is rude. Here, if he said something and you said "could it be the fuel pump" that should also be an inoffensive comment, not prompt him feeling like "how dare this fool presume to lecture me about the inner machinations of an automobile; let this mark the end of our friendship"

I dunno man, I think this is more for situations where people are having personal or emotional issues. Things that they might be trying to work through. Not for troubleshooting a broken car or computer.

Zen and the art of motorcycle maintenance explores exactly this beautifully.

Unasked-for advice is often not actually helpful and more about the advice-giver than the receiver.

They would probably not say that and just slowly freeze you out of their social life because they found you annoying, grating, or unpleasant to interact with.

People often simply want to share what's going on and be heard and recognized. It's a basic human need.

Obviously it all depends on the situation.

Can you imagine the reverse scenario, people giving you unsolicited advice?

Most people just don't like advice they didn't ask for.

Does that "most" mean 60% of people, or 90%?

Unsolicited advice only annoys me if it's long-winded and preventing me from doing something else.

Also, I don't know what "validation" is in this context. Oxford English Dictionary doesn't seem to adequately cover psychobabble (though it does at least have the word "psychobabble").

Do you need a coach to fix your car? Almost certainly no.

If you’re trying to be absurd or sarcastic then I think you need someone like me to help you with that, and I won’t.

Maybe try to establish whether it is something they could fix themselves first?