It is not all about stamina, and it is not all about your team. Opponent team has stamina too, you dont know how they prepared. And its not only about stamina, there is form, if you have form like W-W-W-W-W your form shall drop down and your players shall start to play bad games, but if your form is L-L-L-L-L your players shall start playing better and eventually you should win (something like that, always check your form and your opponent form before match).