The Portuguese boss has come under criticism for failing to include midfielder Juan Mata in the starting squad on a number of occasions.
"It's not easy for me to leave players at home and on the bench because everybody deserves to play," Mourinho said in a press conference. "I'm unfair with the players I am not selecting because they are doing everything to play.
"It's a difficult feeling for me. All of my players have a collective soul at the moment. That's the most important thing."
The Blues are preparing to take on Newcastle United tomorrow.