Again, going back to Erlang, the original base concept of OO was message passing, something that Erlang does very well.
One of gripes of Alan Kay (Smalltalk man) is that the term 'Object Orientated' was 'stolen' by certain language promoters (C++, correctly, says its a multi-paradigm language) - Java! - got into this stupid 'Is-A' hierarchy game, rather than pick up the core concept - messages between objects.
OO is used for simple problems. Without messaging, OO does not scale that well.
*WITH* multiple-inheritance your risk having a complex fckup.
C++ naively supports multi-inheritance in the language. M-I should onyl be used carefully.
Java saw the problems and dodged it slightly.