From a great interview in Wired by Steven Levy:
Our first shareholder letter, in 1997, was entitled, “It’s all about the long term.” If everything you do needs to work on a three-year time horizon, then you’re competing against a lot of people. But if you’re willing to invest on a seven-year time horizon, you’re now competing against a fraction of those people, because very few companies are willing to do that. Just by lengthening the time horizon, you can engage in endeavors that you could never otherwise pursue. At Amazon we like things to work in five to seven years. We’re willing to plant seeds, let them grow—and we’re very stubborn. We say we’re stubborn on vision and flexible on details.
In some cases, things are inevitable. The hard part is that you don’t know how long it might take, but you know it will happen if you’re patient enough. Ebooks had to happen. Infrastructure web services had to happen. So you can do these things with conviction if you are long-term-oriented and patient.