Two brilliant quotes from Alan Kay in 2003:
OOP to me means only messaging, local retention and protection and hiding of state-process, and extreme late-binding of all things. It can be done in Smalltalk and in LISP. There are possibly other systems in which this is possible, but I'm not aware of them.
But just to show how stubbornly an idea can hang on, all through the seventies and eighties, there were many people who tried to get by with "Remote Procedure Call" instead of thinking about objects and messages.