regression - How do I explain the line of best fit in this diagram? - Cross Validated

I teach an intro statistics class at my university (as a graduate student) and I was scouring the internet for interesting graphs on the history of linear regression when I came upon this picture

Learning Curve — Yellowbrick v1.5 documentation

Train/Test Split and Cross Validation in Python, by Adi Bronshtein

Principal Component and Partial Least Squares Regression Essentials - Articles - STHDA

How to Interpret Adjusted R-Squared and Predicted R-Squared in Regression Analysis - Statistics By Jim

7 of the Most Used Regression Algorithms and How to Choose the Right One, by Dominik Polzer

regression - Line of best fit does not look like a good fit. Why? - Cross Validated

IJGI, Free Full-Text

4. Regression and Prediction - Practical Statistics for Data Scientists [Book]

A Beginner's Guide to Regression Analysis in Machine Learning, by Aqeel Anwar