“Men, it has been well said, think in herds; it will be seen that they go mad in herds, while they only recover their senses slowly, one by one.
During the great plague, which ravaged all Europe, between the years 1345 and 1350, it was generally considered that the end of the world was at hand.
‘But the facts, my dear fellow,’ said his friend, ‘the facts do not agree with your theory.’ ‘Don’t they?’ replied the philosopher, shrugging his shoulders, ‘then, tant pis pour les faits’ – so much the worse for the facts!”
Charles Mackay, 1841
https://www.gutenberg.org/ebooks/24518 “Memoirs of Extraordinary Popular Delusions and the Madness of Crowds”
“Establishing the hidden communication networks in large self-organized groups facilitates a quantitative understanding of behavioral contagion.
An individual will be more likely to respond (is more susceptible) if it is strongly connected to the initiator (short path length), and if it has neighbors which are strongly connected to each other.”