Something Else Terrifying

"Diomedes' period of rotation was only twelve and a half hours, and this latitude, thirty degrees north, was still on the winter side of equinox; so the sun was toppling seaward with dreadful speed."
-Poul Anderson, The Man Who Counts IN Anderson, The Van Rijn Method (Riverdale, NY, 2009), pp. 337-515 AT III, p. 354.

Nicholas van Rijn puffs, roars and stumps on-stage in Chapter III.

Add up the environmental factors:

horizon twice as far away as on Earth;
impossibly short days;
sun that looks as if it is falling out of the sky;
flying natives who can swoop down from several kilometers high;
poisonous native food;
immunization needed just to breathe the air or drink the water.

Human beings would feel small, exposed and threatened all the time.