Answer:
Amazon succeeded in the early days of the internet because it found a niche that had a demand for a specific product: books, and made sure to provide a new service: online book selling, as efficiently as possible, taking into account aspects that customers value highly like delivery time, customer assistance, and variety of titles.
Amazon put these principles in practice, and with time, it became larger and larger. Nowadays, Amazon is the largest online retailer in the world, and sells not only books, but practically everything, from food, to technological gadgets, to even cars.