Basically any convex shape has a big/small size configuration in which one doesn't fit in another
Or in other words: if you can't draw a line between the center and the edge that intersects with another edge, the shape is guaranteed to fit a smaller version of itself
My guess would be that after we get scared the brain goes "good job, you survived, here's some endorphins". That way we enjoy getting scared because happiness follows
I'd advice against it, aside from spam filters, and it being a general PITA, there is a chance your ISP will block any outgoing mail traffic (in my case orange blocks it)
Basically any convex shape has a big/small size configuration in which one doesn't fit in another
Or in other words: if you can't draw a line between the center and the edge that intersects with another edge, the shape is guaranteed to fit a smaller version of itself