For every show you check off, this looks at what was played and compares it to how often each song shows up in the catalog from your first show onward (so songs that hadn't debuted yet don't count against you). Expected = how many times you'd typically catch a song if you'd attended that many shows at random from that window. Outliers are the songs furthest from that expectation — your lucky charms (seen far more) and your white whales (seen far less).