It's important to remember that "80% chance you do X" also means "20% chance you DON'T do X". And "20%" means "1 in 5". We like to conflate large percentages a

It's important to remember that "80% chance you do X" also means "20% chance you DON'T do X". And "20%" means "1 in 5". We like to conflate large percentages as "practically 100%" but even ".1%" just means "1 in 1000". For large groups even low percentages can represent a significant quantity.