As we get closer to a world where our own ability to create world-simulations approaches verisimilitude to our 'real world', it becomes more likely that we are ourselves in such a simulation.
Some people find this idea existentially-threatening, but if it's any consolation, those running the simulation can't be sure they're not in a simulation either.
For example, let's say we're inside a simulation run by a race of hyper-intelligent turtles, whose universe simulation, after a few tredecillion ticks, has given rise to our current perceived reality.
Well, it's turtles all the way up.