I got good grades in college and retained none of the information. Perhaps it was because the tests were open book and I am good at applying rules to a given p

I got good grades in college and retained none of the information. Perhaps it was because the tests were open book and I am good at applying rules to a given problem, but my memory is terrible. Now I want to be able to derive everything from as close to first principles as I can. Then if I forget I can recreate the material.