For the challenger Condit, Saturday's matchup marks a chance to seize a golden opportunity and capture the greatest honor that an MMA fighter can achieve.
For St-Pierre, the fight is just another step toward becoming the greatest mixed martial artist of all time. With six title defenses already to his credit, GSP is cemented as a legend in the sport, and it is ignorant to argue that he is anything but the greatest welterweight that the UFC has ever seen.
A win over Condit will simply put him one step closer to Anderson Silva and Fedor Emelianenko in the "greatest of all time" talks. This is unquestionably a huge achievement and motivation for GSP, but his legacy as the greatest welterweight of all time is already confirmed until proven otherwise.
While catching up to Silva and Fedor in terms of being the pound-for-pound G.O.A.T. is a stretch even with a win, it becomes an impossibility with a loss. Should Condit knock him out, submit him or edge him in a judges' decision, GSP can never become the greatest of all time.
His win streak will be halted at nine, and with so many decision victories littering this list, fans and critics will happily dethrone him in favor of guys like Silva, Emelianenko, Jose Aldo and Jon Jones when push comes to shove in the debate.
Put plainly, if GSP loses, he is the greatest welterweight of all time, nothing more...and that's not a bad thing by any means. Realistically, he will not catch up to Silva's ridiculous 16-fight winning streak, and he will probably not defend his belt ten times as Silva has, either. In these respects, nothing is lost as far as his legacy is concerned.
What a loss to Condit does ultimately foil, however, is the possibility of a GSP/Silva showdown in the near future. With a win over Silva, GSP would have to vault up the G.O.A.T. rankings regardless of the numbers that show otherwise. A head-to-head matchup negates all quantitative metrics, and if GSP could defeat Silva in the cage, it would be impossible to deny him as the greatest.
This, of course, hinges on GSP beating Condit.
If "Rush" wishes to eclipse his status as the greatest welterweight of all time and become the greatest, he has to beat "The Natural Born Killer."
Should he lose, his legacy is much, much simpler to define.