That's fine if you're a student and can consistently do textbook problems. What happens when you enter the workforce where you very likely will not use most of

That's fine if you're a student and can consistently do textbook problems. What happens when you enter the workforce where you very likely will not use most of the mathematics and get married and have kids? You don't have time to solve those problems. I had lost all hope till I started using spaced repetition to relearn what I'd forgotten. Is it as good as doing textbook problems? No. But it's better than not doing anything. With spaced repetition I can have gaps of months at a time and can still get back to the material without having to start all over.