: It has supplanted the Encyclopedia Galactica because it is slightly cheaper and has those friendly words on the front.

: Printed on the cover to keep interstellar travelers from panicking when faced with the device's insanely complicated operation.

The words famously inscribed on the cover of the fictional Hitchhiker's Guide to the Galaxy are which the protagonist Arthur Dent describes as "the first helpful or intelligible thing anybody's said to me all day".

While the fictional Guide itself is an electronic device described as looking like a "largish electronic calculator" or a "small, thin, flexible lap computer", the real-world books are often published on and frequently feature this slogan in "large, friendly letters" on their covers to mirror the in-universe description. Key References to the "Helpful" Nature of the Guide

: Famed science fiction author Arthur C. Clarke once noted that "don't panic" was perhaps the best advice that could ever be given to humanity.