There is nothing like the pleasure of using the right tool for the right job.

Using C++, Java or even Python for highly concurrent and fault tolerant systems is a bit like hammering screws into the wall. It can be done with enough effort -- but try a screw driver drill and see what a difference it makes.

The secret sauce is all about fault tolerance, everything else amazingly and logically leads from it: isolation, hot code reloading, distribution (running nodes on multiple machines)