Maurizio Sarri was angry with the sloppiness of his Napoli side despite their 3-1 Champions League win over Feyenoord.
The Serie A leaders were cruising to a 3-0 victory when they conceded a consolation goal to Sofyan Amrabat in stoppage time, having earlier required Pepe Reina to save a penalty before Jose Callejon's clinching goal.
And Sarri feels that the small margins of European competition mean that Napoli cannot afford to continue giving away needless chances.
"At this time, I am much more annoyed about the goal we conceded," he said. "In a competition where goal difference counts, you cannot concede a goal like that 10 seconds from the end. I cannot be satisfied.
"We had a good game, created a lot, but what I don't like is that we allowed Feyenoord absolutely nothing and yet they scored a goal and had a penalty. Clearly, we are doing something very wrong.
"We also should have scored more goals, considering the chances we had."
Both Lorenzo Insigne and Dries Mertens dedicated goals to Arkadiusz Milik, the Poland international who has damaged cruciate ligaments for the second successive season, with Mertens ruing his team-mate's "incredible" misfortune.
"The celebration was for Milik and we played for him, too," the Belgium forward told Mediaset Premium.
"It's incredible to see such bad luck and this is a difficult time for him - so the goal and the win were for him."
