...what didn’t change much was the fundamental lessons: have a diversified portfolio, don’t buy more house than you can afford, don’t take on more debt than you can support, or trade on the margin.
These are hopefully just common sense but of course we know that for many people this was not common sense. I can see a big big problem coming with people spending beyond what their savings can safely generate. My thought all along has been 4%, or less, of whatever you got (more like withdraw 1% every quarter). I'm not real clear on where the willingness to take huge risks with withdrawal rates comes from but I think the willingness to take a lot of money out "now" and hope for the best or expect to take out less later or something else is going to do a lot of people in.
Even in the best of times, or perhaps more appropriately worded in very normal times, plenty of people spend their way to financial oblivion. I can tell you first hand this is very difficult for people to grasp. To the extent that a lot of people have these blinders there stands to be societal problem waiting for us at some point along the lines of the US government spending too much or the problem that might be awaiting the entitlement programs.
I do not do a good job of explaining the potential consequences of this to the people who need to hear this the most. The more you take out the further you are pushing the envelope. Taking 10% out at age 62 for a "one time" thing that coincides with a nasty market decline could become a game changer before you even get started. A slight tweak up to 6% withdrawal rate could become a game changer.
I suspect that this sort of behavioral issue does more people in than poor performance. Maybe people live $200,000 lifestyles when then work but only save for $80,000 lifestyles in retirement and they just don't realize it but whatever the case this afflicts many people. I think it would be much easier to alter the behavior than get better returns but altering behavior might itself be too big of an obstacle.