Not to rain on any parades here, but maybe I’ll play devil’s advocate a little…
The problem with the gods of compounding is that most people don’t have much money to spare at the beginning of this magical 20 years, they are busy getting married, setting up home, having kids etc. They are also at the beginning of their careers and are not usually anywhere near their maximum earning capacity. So they can only put a small amount of money in to the magic compounding machine.
Jump forwards 20 years or so in a successful career and the house is paid off, the kids have left and the earning capacity is massive, and with relatively few outgoings, you can seriously add to your retirement savings.
I started a pension in my 20s, but the proportion of its final value in my 50s is maybe 25%. The rest I added in the last 5 years and compounding had little to do with it.