[gwern]

What I'm saying is that before Bitcoin no one had a good idea for a distributed e-cash which met the basic criteria of no trusted third parties. Given such a system, then you can fairly easily imagine building an anonymity layer on top of it: if nothing else, to name only the very most obvious solution, people can use a mixer service hosted on a Tor hidden service. The jump from ???->Bitcoin is much bigger than Bitcoin->Bitcoin+Tor, and with a working system, one can go back and look at all the fancy anonymity-related math and ideas which had been published or speculated about in the past and see which can be added in, and dollars to donuts, at least one will work and that's all you need. Any group smart enough to invent Bitcoin would be able to foresee that at some point, anonymous currency would follow as a consequence and I believe Satoshi said as much somewhere (although I don't have a quote on hand).