Harry Kewell feels silly mistakes cost his side in the Emirates FA Cup first-round defeat to Barnsley on Saturday.
Second-half goals from Cauley Woodrow, Zeki Fryers, Brad Potts and Kieffer Moore saw Notts bow out of the competition in front of 670 travelling supporters.
And the Australian feels the result was largely down to errors made by the Magpies.
“Two mistakes put us 2-0 down very quickly after half-time,” said Kewell.
“At that point it’s an uphill battle because we had to push forwards trying to get back into the game and left ourselves vulnerable.
“We need to ensure we concentrate for the entire game and cover for each other because we’re making too many errors right now.”
Notts put in a good first-half performance, matching the Sky Bet League One side in the opening 45 minutes, and Kewell felt his side could’ve led at the break.
“We were strong and created good chances before the interval and restricted them to very little,” he said.
“Nathan Thomas had a great chance and Jamie Turley nearly scored with an overhead kick but if you don’t take these opportunities then you leave yourself open.
“Against a team with the quality of Barnsley, you need to convert your chances because, except for Moore blazing one over, we probably did enough to lead at half-time.”
The display before the break gives Kewell confidence for the future.
He explained: “To perform the way we did in the first 45 minutes against a team of Championship calibre is excellent.
“Barnsley aren’t going to be in League One for very long and we held our own against them in the first half so it’s frustrating we conceded two goals in such quick succession.
“We’ve got a huge game coming up against Cheltenham in the league next weekend and we’re relishing the challenge.”