I have recently gotten into statistics and bought three textbooks:

Causal Inference in Statistics: A Primer

The R Book

Pattern Recognition and Machine Learning

I seem to be able to be disciplined enough to learn about small concepts (e.g. exogeneity, synthetic control) through journal articles and Wikipedia, but I have never worked through a whole textbook by myself before.

For me to have "completed" a textbook, I should have read all of the chapters that contain content that I don't already know and done at least 50% of the exercises in the book.