Dortmund management must change their attitude if they want to bring the Bundesliga title in the coming seasons because if they continue to sell star players, it is possible that Dortmund will fast for the title for the next 5 seasons. 10 years is quite a long time but Dortmund have always failed to break Bayern Munich's dominance in the Bundesliga.
Well it is pretty easy to say "change your attitude" but in reality i think it is very very hard for Dortmund to close the gap to Bayern Munich or to even overtake them. The sad truth is that Dortmund is very far away from Bayern Munich both in terms of financials and also in terms of International standing and prestige. Dortmund is not considered a top ten club in the world that is the reason why they can not get the very best players. They buy young and promising ones most of the time. If those are doing very well then they will leave the BVB again for a better club.