The young Wolves side were on the wrong side of a seven-goal thriller at AFC Telford and Sellars believes his side were unfortunate not to take something from the game.
He said: “I think it was frustrating really because, overall, we’ve had more chances and better chances.
“On the day I just don’t think we’ve defended well enough as a team or individually to stop their goals.
“I felt their goals were a little bit easy at times.
“I was really pleased with some of our football and some of the individual performances going forward, I just think we let ourselves down defensively."
The Under 23s Coach explained that his side need to react better after conceding goals.
“After scoring a goal and looking fairly comfortable, the shock of losing two goals knocked them a little," he said.
“I just think the reaction to disappointment for some of the younger players has got to improve.
“It’s part of football, you’re going to concede goals and you’re going to lose games.
“We did that three times; we got back to 2-2 and instantly conceded then got back 3-3 and instantly conceded.
“Mentality-wise, there’s still a lot to learn and a lot to develop over the year.
“What was disappointing was that we went from looking solid against Villa to feeling like something might happen every time Swansea went forward.
“But, overall, as a performance I was really pleased with them, in terms of the things we work on and in terms of spirit amongst them.
“It’s mostly just individual errors that’s cost us on the day. And that’s something we need to improve on."
The Under 23s now look ahead to the next Premier League 2 fixture against West Bromwich Albion at Molineux on Friday ahead of Tuesday's trip to Chesterfield in the Checkatrade trophy.
“This is more of what I want for the lads," explained Sellars before adding: That first team frequency of Sataurday, Tuesday and Saturday games.
“There will be one or two changes for the games and a couple of the lads will be away on international duty next week.
“That then provides other lads with an opportunity to come in and stake their claim.
“We look like we’re going to be a strong team this year.
“If we can cut out some of the individual errors, I think we’ll score goals and I think it’s an exciting group.
“The transfer window is still open so one or two might go out on loan. We’ll have a look at that if we think it’s the right thing for the player.
“Speaking on behalf of the group I think this is the most confident I’ve been since I’ve been here."
