Our friend Mike Long chimes in:

One more:
Who can forget how the left insisted Star Wars was impossible? When I was in graduate school in physics (at Vanderbilt in the mid-80s) a professor insisted to me that strategic missile defense was impossible. I replied—first year grad student bravery/foolishness—that I had long been taught that in science, you never rule out anything up front; that the only new discoveries come from people who do what others say cannot be done.
He got, umm, angry at that.
“Well, this thing is impossible,” he said to me. Gave me s**t the rest of the semester, too.
Hope you’re well.
Best,
Mike L.