I believe in multiple universes too; simply because of the low probability of our universe coming to be at all. It's like this: with one universe, it's a bit like you're rolling a fucking 900 billion sided die, hoping to land on a 1 for life. Now, if you roll the die infinite times, the chance of reality sustaining life goes up to 100 percent, and since other shit can happen after the constants deciding if it's possible are set, each reality would have its major differences. That's not my main reasoning, but I think it's the simplest one to portray, though logically not super strong. (edited)