Mourinho's teams are always successful because he simply won't put up with any passengers. Mata's an excellent footballer, but he doesn't do that much of the dirty, gritty stuff.
Allowing one player to slack off can affect your whole team's mindset. Having a team of fighters makes every game a challenge for your opponent.
This is what's been letting us down a lot recently. The players don't put in enough hard work and don't believe that they can rescue negative scorelines.
I mentioned something similar to this in that our players aren't professional enough. There's too much "banter" and happy-go-lucky mind-sets that I think proves somewhat costly on the pitch. I initially thought having a close knit bunch of guys who have a laugh was a major positive, and while it still has it's plus points, I think they're not used to having strict regimes and don't have the mental strength to know when it's time to have fun and when it's time to put in a real shift. When you look at the top teams and especially the top players, you generally hear how they're putting in a real shift in training and usually staying behind for extra practice, I wonder how many of our lads do that? Brad mentioned on MOTD that Harry asks him to stay behind for extra shooting practice pretty much every day and ironically Harry has been our best player so far, if the rest of the players can follow in his example I'd like to think we'd see a vast improvement on the pitch.