While the question of could Germany win has been asked it seems perennially, this is a slightly different tack. Essentially what is being asked is were there things the Germans could have done sufficently better or mistakes that if they had not happened would have allowed the Germans a win to WW 2?
Now, I'm not talking about the often brought up impossible stuff like tripling production suddenly or having some flegling technology suddenly become practical and in widespread use years ahead of its original introduction but more mundane things that the Germans simply did badly that squandered the possibility of winning.

For example, allowing Himmler and Göring to form "private" armies in parallel with the Wehrmacht (eg., the SS and Luftwaffe ground army). These were massive wastes of manpower and material. There was no justification of either beyond the private empire building of the two people running them.