The a typing feature[1] in the language Eiffel was based on the assumption of the author that the typing holes it apparently introduced could be statically detected. It turned out he was wrong after the language was released IIRC. I guess you have to be pretty certain of something before basing a language around it.

On top of that being a generally shite language doomed Eiffel.

[1] IIRC again, you could cancel features in subtypes, so "all birds can fly" but "penguins are birds but can't fly". That would break the Liskov Substitution Principle, which Bertrand Meyer thought he could deal with but apparently couldn't.