Borussia Dortmund CEO Hans-Joachim Watzke believes the club have paid the price for humiliating Bayern Munich 5-2 in the 2012 DFB Pokal final.
Dortmund has since lost Mario Götze and Robert Lewandowski to Bayern, while Marco Reus could join them next summer.
"The decisive mistake was that we scored two goals too many in Berlin," Watzke said at the club's general assembly.
"Bayern could have accepted a 3-2 defeat, but a 5-2 loss was too much for them.
"Bayern's dominance in Germany is down to their expenses on players."