You teach Calculus? Then you should write Hard SF.
I’ve seriously been told this. By a major book company editor.
The truth is, I have no interest in writing an SF novel about Calculus. Nor do I think I would read one. And honestly, if we all wrote what we knew, we would only be writing diaries and journals. All fiction is just that….fiction.
Am I saying we don’t need to know anything before we write? Not at all. We need to put thought into our work. And yes, it truly helps if we learn to do things first hand. (Otherwise all my time learning fencing, horsemanship, shooting, rapelling, sailing, camels, languages, etc…was all wasted.)
But I write about sereia and selkies and seers. Do I know any of these personally? Have I interviewed any of them prior to writing? I’m afraid not.
And that’s a part of what makes writing (and reading, I hope) fun.
So if you want to write about submarines or dirigibles, you don’t have to build one first. Do your research, but don’t let the fact that you’ve never captained a dirigible stop you from writing that…