[hota_mazi]

But that's what polymorphism does.

Somewhere deep in the code is calling a.foo(), but when you pass a subclass of A that overrides foo(), then this code "magically" calls that new implementation.

This is where specialization shines and no other paradigm allows this so elegantly and so simply.

[aflag]

That is not exclusive to OO and it wasn't invented by OO either. However, the common pitfall of changing the implementation of a method that was not designed to be changed I would argue to be more common in OO than in other paradigms. That's a common pitfall, though. Not a place where OO shines. Though, to be fair, that's a problem in Java, Python and other popular OO languages, but not inherently a problem of the paradigm per se. C++, for instance, avoids that common issue by not making methods virtual by default.