I don’t think we suspected the Ruskies could shoot down a U2 either in the late 50s. Never underestimate the enemy.
A long ago mentor of mine gave this advise more than 50 years ago: guy comes up and bets you he can jump over a building, don’t bet. Never make a bet with someone who sets the object.
As I recall; so-called experts also claimed the Berlin Wall wouldn’t come down until the bricks started hitting them in the heads.