How crucial stamina training is?
I mean, I've just got a team and most of my players are wretched at it.
Their performance will deteriorate throughout the game.
One oddity is that if your players don't have good stamina, they will be substituted for more often. On a new team, you may think you are doing a good job on getting training minutes for everyone. But then when your starters get more stamina, they may play most of the game.