Perhaps a wiser phrasing would be “a language’s interface should be simple enough that the programmer should be able to know everything about it”. (Counterpoint

Perhaps a wiser phrasing would be “a language’s interface should be simple enough that the programmer should be able to know everything about it”. (Counterpoint: C++ syntax and semantics.) The internal implementation can (and usually will be) heinously complicated but as long as it adheres to that external contract any nasty surprises are ones users create for themselves, not the language’s doing.