Why did Java and C# add intrinsic lock to every object?

Question

Making every object lockable looks like a design mistake:

1. You add extra cost for every object created, even though you\'ll actually use it only in a tiny fract

Answer 1

Actually you only have reference to that monitor in each object; the real monitor object is created only when you use synchronization => not so much memory is lost.

The alternative would be to add manually monitor to those classes that you need; this would complicate the code very much and would be more error-prone. Java has traded performance for productivity.