In every single case, the Scooby Doo gang discover a human is behind the mystery, not ghosts or mummies or whatever. Yet they start each new case believing the villain is a supernatural being. Every time. Not once do they say “maybe it’s an old man like last time”

@JoParkerBear
I've oft taken that as an indication that being continually stoned has limited their conversion of short-term memory to long-term.

That or they're just joking around and having fun (despite the shrieks and endless cardio) because they know, based on basic pattern recognition, that they're not really in any danger.