I think the reviewer Derek Pillion summed up this book rather well. But I want to relate something that came into my mind after reading the following passage from chapter III:
"A hundred petty crimes or petty accidents will not strike the imagination of crowds in the least, whereas a single great crime or a single great accident will profoundly impress them, even though the results be infinitely less disastrous than those of the hundred small accidents put together.
The epidemic of influenza, which caused the death but a few years ago of five thousand persons in Paris alone, made very little impression on the popular imagination. The reason was that this veritable hecatomb was not embodied in any visible image, but was only learnt from statistical information furnished weekly.
An accident which should have caused the death of only five hundred instead of five thousand persons, but on the same day and in public, as the outcome of an accident appealing stronly to the eye, by the fall for instance of the Eiffel Tower [sic], would have produced, on the contrary, an immense impression on the imagination of the crowd.
... To know the art of impressing the imagination of crowds is to know at the same time the art of governing them."
What came into my mind after reading that passage? Airplanes and collapsing towers. This book is a must read for any thinking person.