Tell me if I'm wrong now , but I've heard that the "why" we dream , is harder to explain than the "how" we dream.

There are all sorts of theories about why , as you probably know , some are spiritual , some are more pragmatic, but one of the theories that always made the most sense to me , was that it was some sort of simulation , as you say , but a way of simulating a dangerous scenario that could potentially happen in real life , and that inside of this simulation , you brain sort of "war games" out these scenarios , and documents the results , so that if something were to happen in the real world , your brain would have already populated itself with data on how things might go , and what to do .