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Andy Hessenthaler admitted Saturday's goalless draw at Havant was a big missed opportunity for Dover.
The Whites boss felt strongly that his side should have taken all three points after Chris Robertson's red card had reduced the home team to 10 after 35 minutes.
The result left Whites 19th in the National League, behind Havant on goal difference, and Hessenthaler said it was two points dropped on a day when none of the five teams below them won.
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He said: "There's a lot of frustration, it was two points thrown away, because we did not deserve to win on that performance, especially in the final third.
"Up front we weren't good enough. I thought Jamie Allen was lively, he caused problems so I can give him a bit of credit but I just felt we lacked that bit of belief and desire to try and put our heads in to go and score, and also that little bit of quality in the final third.
"I thought we were actually better when it was 11 versus 11, we dominated the first half we were well on top without really creating enough chances and (without) enough real belief and that final bit of quality, we just couldn't find that today.
"(We made) poor decisions with the football, we tried to change it, to try to create more overloads in wide areas but there were balls going in there, and they (Havant) anticipated better than we did and that's disappointing for me.
"I know we've only lost one game in 11, but we don't want to rest on that, we needed to get a result today.
"Give Havant a lot of credit, we did it last week, we had nine men for 40 minutes (in the 1-1 home draw with Bromley), and they've had 10 men for nearly 60 minutes.
"They dug in, they're fighting for their lives like we are and they deserved to get something out of the game. "
Dover's two best chances fell to Jai Reason, and Hessenthaler felt the midfielder should certainly have scored from the second, when he was denied by Havant keeper Ben Dudzinski's block.
Hessenthaler said: "He's got to score, and I've just said that to him in the dressing room.
"I expect him to score especially the second one. For the first one he's made a great run, it was a great ball and perhaps he got too much on it, but the second one, it's actually a fantastic bit of play in terms of the way we opened them up.
"That was the only time in that second half we had any type of movement and cleverness, it got us in but Jai hit it straight at the keeper. I really fancied him to score because he has got that bit of quality."
One big plus for Hessenthaler was the performance of 20-year-old loan signing Danny McNamara, who capped an encouraging debut at right-back with an injury-time goalline clearance to prevent the home side snatching an improbable win.
Hessenthaler said: "I thought he was excellent, for his debut, not knowing the players that much, in a tricky game because of the position both teams were in, and the conditions I thought he was fantastic.
"I did my homework. I spoke to Kevin Nugent (Millwall's under-23 manager) and 'Chopper' (Millwall manager Neil Harris) who I speak to all the time and they said we all love him, and he showed all of what they told me he could do."
Midfielder Bedsente Gomis has been given a three-game ban following his red card against Bromley.