The Toffees were beaten 2-0 by the Championship side in the third round of the EFL Cup at Goodison Park on a night where the home team certainly had their goalscoring chances.
Koeman says his side must not dwell on the negative result, as they were slightly unlucky not to have found the back of the net, and now have to pick themselves and prepare for the weekend's Premier League clash with AFC Bournemouth.
"Of course I'm not happy about the final result because in cup football you don't get a second chance," said of the Premier League's second-placed team.
"But I can't criticise my players because they did everything to score the goal.
"We had enough chances to score the goal but we did not. You can make it difficult, but football is about scoring goals and, as you saw with the first goal for Norwich, you need a bit of luck.
"I don't organise parties after 13 points from five games or have gripes after tonight. It's football and we have to accept it. We are disappointed but from [Wednesday] we will prepare for the game against Bournemouth and we go on."