Run what you brung 

A term used for street races, where you accept the results of a race instead of making theories how the race could have turned out differently.

Guy 1: "That Supra would have beaten that ZR1 if it had a bigger turbo."
Guy 2: "Who cares about your fantasy racing? That Supra didn't have a bigger turbo. It's run what you brung!"

can be applied the other way too:

Guy 1: "That Dodge Charger SRT8 would have won against that WRX if he had used racing slicks."
Guy 2: "Who cares, he didn't race with racing slicks so he lost. It's run what you brung!"

Run what you brung by Chris brown is Lame June 7, 2012