Roberto Mancini could not hide his frustration after City left the Stadium of Light empty-handed on Sunday.
The Blues failed to take several gilt-edged chances in the first half, most notably one that fell to Carlos Tevez, and this came back to haunt them when Darren Bent buried a penalty past Joe Hart in stoppage time.
"Football can be very strange," said the Manager, "we played some fantastic football in the first half, we had three or four real chances but if you don't take your chances sometimes it can happen that you lose like this.
"Carlos had his chance, we had some others but that's how football is. All the games are difficult and you have to play until the end, to the very last second.
As for the penalty, from the bench it is difficult to say whether it was a penalty or not.
...Boss on defeat at Sunderland
City were not as strong after the break and Mancini was at a loss as to why, with added frustration given that he will now not have his full squad together until just before the next game against Blackburn Rovers on 11th September.
"It's hard to say why now, I want to speak with the players when they come back from the international break because in the second half we were split in two or three places. We made it too easy for Sunderland, but I don't know why.
"I am frustrated because now we have two weeks before we play again. It's better to go into a break with a win or even a draw, but after the first half today, I would not have thought we could have lost this game.
"It's vital we understand why we lost this game because there will be times when the other team plays 10 men behind the ball. We must be patient, but if we don't take our chances we will make it hard for ourselves."