This is a great article. It gets at something I've been thinking about myself.
One of the common arguments I've seen for the 4% rule is that it would have worked through everything the 20th century could come up with: depressions, stagflation, two world wars, an oil crisis, etc. As long as you assume the future won't have anything worse or dramatically different than what came before, your success is all but guaranteed.
But there is something new in the world, and it's us, the Mustachians. We invest in a way that's very different from most groups of investors that came before. We're more patient, less reactive, less prone to wild swings of sentiment. And the more people see that it's working for us, the more of them will follow our lead.
I realize this is an exaggeration. There aren't enough of us to move the needle on the entire stock market. But there are also big players, pension funds, endowments and the like, that are adopting a similar strategy, switching from active management to passive indexing. That can't help but make a difference to the way markets react. The knowledge of how to extract a predictable profit from the stock market's irrationality is itself a factor that's changing the behavior of the market.
Obviously, if this is a trend, it's a brand-new one, so it's too soon to draw any long-term conclusions. I doubt the future will be a smooth slope of ever-higher valuations and ever-decreasing volatility. Herd behavior is a powerful force that won't go away. Nevertheless, we should consider that previous experience may not have prepared us for what the market will do in the coming decades. The old rules-of-thumb may not work anymore.