Remember the good old days of DOS, when you could open command.com with a simple text editor and find the line with the dreaded "Abort, Retry, Fail" message.
Unwary users were so supprised to see "You're F!*%ed" or some such. And no ammount of rebooting would solve the problem.
The strict control of clock and data timing leaves little margin for error in a DDR SDRAM interface. Testing of these interfaces demands adherence to some important best-practices to ensure accurate and repeatable results.