It's not a simple hypothesis, and it's extremely lazy pedagogy. It's not a reasonable guess if you can't establish any reasoning that would lead you to it, and

It's not a simple hypothesis, and it's extremely lazy pedagogy. It's not a reasonable guess if you can't establish any reasoning that would lead you to it, and even if you could, in a textbook, I expect your guesses to be more than reasonable, I expect them to be actually reasoned.