Also, some people just want a faster horse

Yes, don't forget if the user asks for a faster horse and you sell them a faster horse you still win.

And you may be able to sell them what they are already asking for a lot faster than what they are not.

Now if you are trying to sell them something that they would rather not even have at all, that's another story too.

Others really want the trebuchet…

That’s fine if the vendor anctually understands the users needs better than they do, otherwise it’s just pure chance if they happen to align.