Could be

They said it was impossible for Cesar Chavez and the United Farm Workers to improve working conditions and wages for the Latino American community.

They said it was impossible for anyone to break the four-minute mile until Sir Roger Bannister came along and did it.

They said it was impossible to put a person on the moon and we know how that story played out.

Perhaps impossible just means, “this has never been done before.”

The gap between “this is the way things are” and the way things “could be” is massive. Although we distort the two.

Unlikely, uncertain, haven’t seen this done may be a better way to describe the situation before us. Impossible means the gap can’t be closed. Improbable means unlikely to close it.

Not the same thing.