Stormers captain Duane Vermeulen was upset with his side's performance on Saturday as they went down 25-17 to the Cheetahs in Bloemfontein.
The Capetonians were eager to strengthen their position at the top of the South African conference in Round Twelve but instead suffered a defeat on the road.
Victory for the Bulls has subsequently seen them reach the summit above the Stormers and Lions, with number eight Vermeulen honest in his assessment.
"It's obviously disappointing and not what we wanted, but we need to learn from games and results like this," he told the Stormers website following the loss.
"Some stupid mistakes cost us and, like I said, we need to learn from this experience and continue to work harder."