Didn't say that, I said that we rarely need parallelization for raw number crunching. Developers use parallelization for coordinating expensive IO way more oft

Didn't say that, I said that we rarely need parallelization for raw number crunching. Developers use parallelization for coordinating expensive IO way more often, and Java 8 streams solve almost nothing for that. Still need to know and worry about other Java concurrency primitives like volatiles, monitors, thread pools, etc. and all their pitfalls (race conditions, deadlocks, etc.). You should still read JCIP, it is still highly relevant in Java-land. Java 8 streams solved almost nothing in terms of concurrency (in fact they probably created more problems than they solved...). You should still be scared of concurrency in general, and particularly in Java. And you should definitely consider a different language with more sane and modern concurrency primitives if you really need concurrency.