There's an old saying that goes roughly: When an old engineer tells you something is possible, they are definitely right. When an old engineer tells you something is impossible, they are only probably right.
"X is impossible with current metalurgy". "Y is impossible with current best integer factorization algorithms".
Absolute impossibilities do exist too, but you basically need to prove that that particular thing goes against laws of physics/maths.
Andy Grove in 1992: "The idea of a wireless personal communicator in every pocket is "a pipe dream driven by greed."
Did he also poopoo the idea of a public internet and wait until the 80s to do so?