The problem with the deal was people's egos trumping over business sense. Dortmund called us up early in the window with smug confidence and said "We know you want him, here is how this is going to work". You only do that when you hold all the cards and have no interest in maintaining a mutually respectful relationship for the future.
United, quite rightly, tried to find a solution to the impasse - probably taking into account the player's availability and willingness to join us. But one Dortmund's so called deadline wasn't met per their terms it simply became an exercise in ego flexing. I still believe we would have got him in the end had United caved to their demands even post the deadline but ultimately it is too much of a risk.
There is a reason why we aren't in a similar financial situation to them or Barca despite having no sugar daddy. We have 0 visibility on how future revenues are going to pan out and to fork out a fortune for an upcoming player who has no experience in the PL was to put all your eggs in one basket and to jeopardize the future of the club. This isn't a casino.