These physicists, Einstein included, have an overblown sense of their intellectual powers. They think they can understand how our Universe works. They will only ever be able to understand a small fragment of it.
They have known for 50 years that relativity and quantum mechanics are incompatible. They hope that superstring theory can be of some help, but probably no one thinks they will ever understand ultimately what the structure of the Universe might be, or if that is even the right question.
Blecchh!
-good times, G.J.P. (Jr.)
On the contrary, we physicists understand much better than laymen how little--or how much--is understood, because we know where the boundaries lie.
It turns out that fundamental questions of how space and time behave are comparatively simple and knowable, and if our answers aren't truly complete, they are very nearly so. Questions such as "how does water flow" or "how do protein molecules get their shapes" or "how do bumblebees keep aloft" or "how does a carburetor do what it does", now, those are hard questions.