He told the club's website: "It was a little bit disappointing. We did not start playing until we went a goal behind, so it is important we start playing when we are 0-0 or 1-0 up.
"We seem to concede and then have a lot of work to do, and you cannot keep doing that in the Premier League, you cannot keep conceding and getting away with it.
"We have been lucky up to now, but that has to stop.
"You cannot really put your finger on why. Everyone is soul-searching to try to find out.
"With all due respect to Sunderland, when you look at the two team sheets, we should be blowing them out of the water.
"For some reason, that is not happening at the minute. But everyone is looking at themselves and at what they can add to it and hopefully, it starts happening sooner rather than later."