Because the future is unknowable^*, people often make claims that it's pointless to analyze the past in order to estimate the future. Nevertheless, these same people do one (or more) of:

• withdraw 4% at retirement (or 2% or 6% or ...)
• invest in x% stocks + y% bonds
• create a 4 x 25 slice & dice
• invest in passive not active mutual funds
• invest in u% domestic + v% foreign
• use annual rebalancing
• etc.

It always seemed strange (to me) that, without investigating the past, they are able to make these choices.

And, as for ignoring all the mathematical gadgetry that is used in investment analysis, it may come as a surprise that devoting a portion of our portfolio to an asset class with smaller returns can actually increase portfolio returns.
Well ... it came as a surprise to me!

One can prove this (with mathematical slight-of-hand and magical assumptions)
or play with an online spreadsheet
or observe it by ... uh, investigating the past:

>So you have faith in that mathematical machinery, eh?
No, of course not. It provides some insight into possibilities and ...
>So what's your point?
My point is that you shouldn't place your faith in a mathematical prediction. Use it as a guide. Think about what it's saying. Don't trust your financial future to some mathematical ritual. Don't ...

>What do YOU do?
When I describe my own investment techniques I avoid claiming that it maximizes the MickeyMouse Ratio or minimizes the DonaldDuck Average (although it's usually more effective to replace Mickey & Donald by a Nobel prize winner, as in Sharpe Ratio).

I like to end up with the phrase: "It's more fun that way!".
>Then, who can argue, eh?
Precisely.
>And your investment technique ... what is it?
As the world's worst investor, I would NEVER recommend my investment technique.
>Gimme a hint, okay?
Well ... okay.