The great baseball player Yogi Berra, who is quoted in the title, succinctly described what it meant to learn something that others had long ago appreciated. The mechanism by which the enzyme chorismate mutase accelerates the Claisen rearrangement of chorismic acid has for many years perplexed and intrigued chemists and biochemists. Yet classical effects of solvents and catalysts, which were largely ignored by the chemical community, not only provided important clues about the mechanism of the enzyme, but put the Claisen rearrangement in a new perspective. Whereas chorismic acid once seemed exceptional because it rearranged so rapidly under physiological conditions, it is now clear that even allyl vinyl ether rearranges at room temperature in aqueous solution. While the ability of the enzyme to accelerate the rearrangement of chorismate by a factor of 106 was once considered extraordinary, catalysis by trivalent aluminum compounds matches, and in some cases exceeds, those rate enhancements. Therefore, it really should not be surprising to learn that Nature has independently evolved several structurally distinct solutions to the design of enzyme catalysts for the rearrangement of chorismic acid.