Very much this! I'm about to start my seventh year, and if all goes well, my last. It's been a blast, and I've learned so much: whenever I've thought to myself

Very much this! I'm about to start my seventh year, and if all goes well, my last. It's been a blast, and I've learned so much: whenever I've thought to myself "gosh, I wish I knew more about ___" I could choose to learn about it from a leading expert, for free. For people who measure their success in dollars earned a PhD is an idiotic investment. About a year ago I calculated the difference in how much money I have, and how much money I would currently have had I accepted an offer from Google after my first year. Obviously that stung a little. But I wouldn't trade the last six years for anything... not even the above-mentioned amount of money ;)