A rivalry makes something that is dull more interesting. When Magic Johnson and Larry Bird's rivalry started every game they played against eachother was very special and attracted some of the highest attention of any sports rivalry ever!
Their NCAA tournament finals broke the record for most watched on tv, and was held for a decent bit longer. Their rivalry was one of the earliest, most documented rivalries ever because the television was gaining prominence as their rivalry gained prominence. It was also one of the most moving rivalries because they went through a lot together and in the end they became the best of friends, the rare outcome for a rivalry. Their rivalry will be remembered as one of the best all-time.