How much value is there in reading without completing exercises? I find that, for myself, knowledge gained through hands-off reading is very shallow and difficult to apply. On the other hand knowledge I've applied hands on has been vastly valuable. One recent example that springs to mind is kmv data sketches. I understood their theory and the algorithm's details but the (simple) concept and it's cases of applicability did not really click for me until I wrote one for use in an application on someone else's recommendation. I spent the next week gushing about my revelation, to my colleagues' annoyance.