[JJStrebas]

I agree that it is up to "you" the author/worldbuilder to establish "the rules" of the story. Part of the fun, for me anyway, when I read a story or watch a movie is to figure out what and why everything is happening the way it does. Particularly in sci-fi or horror, of course.

Some leap of faith is required, I think. A while back I was reading something where some brainiac theorized that a monster like Godzilla (or maybe it was King Kong) would be impossible because their bone density would never support such weight and just taking a few steps would be crippling and merely breathing would be difficult.

I kinda think the "same" would be true for really tiny people. They would be super fragile and delicate. Nature has designed bugs the way they are for a reason (exoskeletons, no lungs, etc) because that is best for their sizes. And they are still very delicate when you try to handle them. We wouldn't work as well being scaled up or down to that extreme.

Tl;dr Setting your own rules for the narrative is part of the fun.