Tourist: This is a dangerously steep road with a sharp bend. Why isn’t there a hazard sign for motorists to slow down?
Guide: We had a warning sign untill yesterday. But since accidents were rare, officials concluded that the spot isn’t that dangerous after all. So they removed the sign.
Tourist: Don’t you think the rarity of the accidents was precisely because of the warning sign?
Amused at the stupidity of the officials? That’s because it’s easy to spot the cause and effect relationship between ‘presence of warning sign’ and ‘frequency of accidents.’ You can test the hypothesis. Remove the warning sign and if too many cars start plunging down the valley, there we have it – a clear correlation between an action and its consequences.