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

Constructing a best fit line

Multivariate Cross-Validation and Measures of Accuracy and Precision

Overfitting and Methods of Addressing it - CFA, FRM, and Actuarial Exams Study Notes

Stepwise regression - Wikipedia

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

K-Fold Cross Validation Technique and its Essentials

Line of best fit (Linear regression) over vertical line - Cross Validated

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

Simple AutoML for time series with Ray Core — Ray 2.9.3

How to Perform LOESS Regression in R (With Example) - Statology

Understanding The Difference Between Linear vs Logistic Regression