> But eventually it was accepted that there are several other, equally valid, geometries, not just the Euclidian.

In other words, they overcame the natural tendency to assume that what we know about a subject is all we need to know.

Maybe it is, in a given case, but maybe it isn't.

You can know that you don't know something (Are there drive-ins in outer space? Let's build rockets and find out!), but there are you *don't* know, you don't know because you don't even suspect their existence.

Mad cow disease is an excellent example. No one foresaw it, or, apparently, could have foreseen it.

Such things are sometimes called "unknown unknowns."