In the 1800's, train speed limits in England were regulated to below 60 MPH because any faster and the air would be sucked out of the passenger's lungs.
The Smithsonian Institution stated after Langley's failures, that man would not learn to fly for 1 million years. They said that months before the Wright brother's first flight in 1903.
In our time, we were told the sound barrier was impenetrable. Resistance to supersonic flight would reach an infinite value at the speed of sound and smash the plane to pieces.
Then they said it would be impossible to fly a manned mission to the moon because of the Van Allen belts.
Feel free to add to this list of scientific "truths".