Shaun Edwards is still experiencing "a bit of disbelief" after Wales outscored England 3-1 on tries at Twickenham last Saturday but still lost.
Wales will finish as RBS 6 Nations runners-up if they beat Italy in Cardiff this weekend.
England, though, have already claimed Six Nations silverware, and they head to Paris on Saturday targeting victory over France to secure a first Grand Slam since 2003.
Wales were punished for a feeble first-half defensive display at Twickenham - they missed 19 tackles - with England going on to lead 19-0 and 25-7 before the visitors scored two late converted tries after Red Rose prop Dan Cole had been sin-binned, meaning the final deficit was just four points.
"We didn't perform well in the first half, but we dominated the second half totally," Wales assistant coach and defence specialist Edwards said.
"To be honest, I am still in a bit of disbelief that you can lose a game in rugby having scored three tries to one. I have tried explaining that to my mother, who is from Wigan, and she didn't seem to understand it.
"We conceded one try away against England. If you look at that stat, it is not a bad performance.
"Technically, there were certain aspects of our defence that I was disappointed with in that first half, mainly the one on one against their numbers 11, 14 and 15.
"But statistically, one try away to England is not a bad effort. Was I happy at half-time? No, I wasn't. Did we perform a lot better in the second half? Yes, we did.
"I am not under any illusions that we weren't on our game in that first half. But I still can't get my head around how you can score three tries, they score one and we lose."
Asked if it was just a bad day at the office defensively, Edwards added: "It would seem that, because as a defence we are still in with a chance of conceding the least tries in the competition.
"We have conceded five, England have conceded four. If we can manage to pull off a try-less game on Saturday, the pressure will be on England to keep France out.
"It would seem to be a bad 40 minutes - we will just have to wait and see."
Wales are now building towards facing Italy - opponents they have never lost to on home soil - but against a backdrop of the Joe Marler-Samson Lee incident at Twickenham continuing to dominate.
The Welsh Rugby Union said on Thursday it is surprised at the Six Nations' decision not to sanction England prop Marler for his "gypsy boy" comment to Wales forward Lee last weekend.
In a statement, the WRU added that the incident had "raised broader issues for the game of rugby" that they are "undertaking directly with the Six Nations".
Edwards, meanwhile, believes England are favourites to make it mission accomplished at Stade de France and end a 13-year wait for a Six Nations clean sweep.
"You can never write France off. I think they have a chance," Edwards said.
"Do I think England are the favourites? Yes, probably. England are probably playing a type of game where they are not allowing their opponents an easy route to the try-line.
"Saying that, we scored three tries against them."
Looking ahead to Italy's Principality Stadium visit, Wales fly-half Dan Biggar added: "You have to move on in professional sport, and we have a hugely important Test match on Saturday where we have the chance to finish second (in the Six Nations).
"It's not what we wanted, but to finish second is still a reasonable achievement. Nowhere near where we set our standard, but that's what we are playing for on Saturday and we have to make sure we give Italy full respect.
"The first 40 minutes (last) Saturday wasn't good enough. We've said that ourselves and players, coaches, the whole staff - everyone has to take that on board. We just need a response on Saturday."