Here’s a quote from a SIAM News article about Peter Lax…

Colleagues remember Peter’s unique style during mathematical discussions. “He was famous for napping while listening to a lecture,” Strauss noted. “But at the end, he would nevertheless often come up with an incisive comment or question.” This apparent contradiction sometimes epitomized Peter’s deep understanding of a topic before the lecture began.

People used to say the same thing about Gene Golub and I observed it myself. Having been in academia a while now, it isn’t ‘deep understanding’ necessarily. It’s that you’ve seen it before (which correlates with deep understanding). So much academic research is simpleminded and derivative and formulaic and doesn’t address the deep problems. So much of it just doesn’t work. So much is repeated. So much can be inferred from past work by the same people. The limitations are often already there and have been pointed out before.