After golf collectively got excited about the prospect of a new Big Three of Rory McIlroy, Jordan Spieth and Rickie Fowler, the world No. 1 quelled that talk with two wins in his last three starts. But here's the thing: There hasn't been a great golf rivalry in the last half-century that didn't involve Jack Nicklaus. We explain why and how it'll be difficult for a great rivalry to ever surface again.