The key is that the memory of these processes is isolated from all the others. Think of how operating system process work. You can restart a small group out of

The key is that the memory of these processes is isolated from all the others. Think of how operating system process work. You can restart a small group out of 1 million and have confidence the rest are not affected. That is a powerful and awesome ability. Imagine you have a million threads all sharing the same data structures with complicated barriers, locks, mutexes, and condition variables. Some subset of them crash, can you confidently restart just those threads? Usually no, because they could have scribble on the memory that other threads will use, or might be holding some lock and such. In operating systems terminology it's like when your calculator app crashed and it took down your word processor as well in Windows 3.1 days.