[throwawayarnty]

Biology is particularly difficult to learn in school or from any book because one cannot “do” much biology on pen and paper.

Math, physics, and certain parts of chemistry can actually be done on pen and paper (or by computer simulations) because it is based on solid theory with mathematical underpinnings.

The only solid foundation biology has is descriptive theories from Darwin and maybe Mendel. All other biology must be studied through experimental data, which means wet lab and analysis. Just reading about a result (which is how school is done) doesn’t mean you are a good biologist no matter how well you can regurgitate the textbook.