Maurizio Sarri has voiced his frustration with Napoli's 3-2 Champions League defeat at the hands of Besiktas.
The Serie A side were in charge for large parts of the game, but were eventually left empty handed at home following a late Vincent Aboubakar goal.
"We are complicating matters for ourselves. We are playing well, but make mistakes at crucial times," Sarri told Mediaset.
"The first goal was a defensive mistake, the second was one where the defence was not involved and we were too naive for the third goal. Plus the third goal was offside as well.
"But I saw progress compared to the game against Roma. We made a small step again."
Dries Mertens put in a fine performance for Napoli, but was unable to help them get a good result and the Belgium international felt Sarri's men were unfortunate to lose.
"We were unlucky tonight," Mertens stated.
"They had three shots on target and scored with all three. It's a pity.
"We missed Arkadiusz Milik tonight, but that is not the reason why we lost, because in the end we had our chances. We had the opportunities we needed to win, but we did not manage to."