One of the most important prerequisites of a success with SuperMemo is the proper selection of the learned material. The art is not to know thousands of facts, but to know just those of them that can be directly applied in the day-to-day activities of the learner. Memorizing a phone number of a colleague may produce more profit than knowledge of a sophisticated mathematical formula. A simple rule for drug application may be of greater use than a hundred of drug dosages. The question: 'What do I want to learn and why?' should be a commonplace in the SuperMemo learner's daily schedule. SuperMemo allows to learn fast, and therefore may easily lead somebody to learn a lot of useless garbage without ever stopping to ask 'What for?' Applicability must be the primary criterion in choosing new items to learn. Applicable knowledge may be a source of hugely increased effectiveness and personal satisfaction for the learner. Garbage items only waste the learner's precious time.