In martial arts, Shodan — the first degree black belt — is not the end of training. It is the beginning of mastery. The same principle applies here.
A SHODAN-level DJ is able to pull of a great 45 minute live set with 30 vinyl records from his crate, but the records are chosen randomly 5 minutes before the set. Demonstrating such skill means you're able to "save another DJ's life" as a last minute replacement. The guests shouldn't notice the performance wasn't planned. The set won't be perfect — but it should still be very good.
Once the DJ achieves Shodan level he or she can continue training even if many years have passed since. Moving further to earn the next "dan" will broaden DJ's music horizons and sharpen mixing skills, regardless if the rank is obtained or not. It is about the journey, not rewards. Tasks get progressively harder across 7 ranks — from playing someone else's records to performing a flawless set with vinyl you've never heard before, brought by strangers.