The invention of the printing press
In 1440 the printing press was invented, before this books were handwritten and a work of art. They had beautiful illustrations and were very expensive treasures and generally for the wealthy.
People often read books aloud, the first book Gutenberg printed was the bible. Before this people had to listen to scholars reading it and suddenly there was a revolution and the press allowed anyone who could read to do so for themselves.
Eventually more books were printed and the price of books became more affordable
Like with the Kindle, critics worried people would no longer read aloud and sharing books would be unfashionable and the experience lost, more importantly to some, the printing press would put scribes out of jobs.
More in line with the critics of the Kindle, they stated the printed books were not as pretty as the original books and an art form would be lost. This was not untrue but the benefits far outweighed the pitfalls.
The availability brought about a whole new age of education, science, arts and religion, it has been called one of the greatest inventions of all time.