Some languages make it very simple to do parallel operations. Java and Scala parallel streams, for example, are like one line of code. Obviously that won't work

Some languages make it very simple to do parallel operations. Java and Scala parallel streams, for example, are like one line of code. Obviously that won't work for all use cases, but when it does, it is simple. Heavily multi threaded code is difficult to write correctly. Do it wrong, you wind up with race conditions, data corruption, dead locks because a thread pool or other resource is exhausted, thread leaks because you didn't shut something down correctly. The problems go on and on.