Extraordinary Popular Delusions and the Madness of Crowds is a study on crowd psychology and is extremely relevant to the present day, despite being written back in 1841. It explores how easily we can be misled and how illogically we can think when popular opinion influences us. The central theme in the book is that the tendency of humans to develop a herd mentality leads to individuals in the herd to act and react to various stimuli. The reactions are very similar and predictable and this “madness” leads to a downward spiral with undesirable effects.