What is the reason that the 10y forward shifted inverted Shiller PE Index predicts the S&P 500 10 year return this well?

External question — Personal Finance Stack Exchange Author: CuriousIndeed Original post: https://money.stackexchange.com/questions/163542 License: CC BY-SA 4.0 — https://creativecommons.org/licenses/by-sa/4.0/ Adaptation: HTML converted to plain text; contact email addresses removed. I was watching a video by game of trades. In the video he argues that the using the inverted Shiller PE Index shiftet 10y in the future can be used to predict the movement of the S&P 500 10 year return. He argues that the Shiller PE can be used in this manner to predict long term market movements of the S&P 500. The chart show quite good correspondence if you want to invest long term. Is this strategy used and is it a valid strategy?