I find a combination useful. The things I read without doing exercises gives shallow knowledge indeed, but that shallow knowledge lets me know what I must lear

I find a combination useful. The things I read without doing exercises gives shallow knowledge indeed, but that shallow knowledge lets me know what I must learn about later when I need it. Also shallow knowledge is easier to obtain, so I can spend time on getting shallow knowledge that would not have been time I could use for real learning because there the limit to how much real learning can be absorbed during say a day is lower than the amount of time available in a day IMO.