Basically Düsseldorf is the state capital, despite Cologne being far bigger and arguably more culturally important, so people from Cologne are jealous. Düsseldorf also historically tried to copy the Cologne carneval traditions. People from Cologne often view Düsseldorf citizens as snobbish and arrogant while people from Düsseldorf view them as boorish, their city more dirty and unkept than theirs.