Cook said his men were hurting 'like hell' after back-to-back humiliations, the latest of which was a 218-run loss to Australia on Monday to slip 2-0 behind in the Ashes series.
"We have to be honest with ourselves, we haven't played well enough in these two games," Cook said.
MORE: Michael Clarke: Hard work paying off in Ashes series | Second Ashes Test: Australia clean up England to go 2-0
"It's hurting us like hell but we're the only guys who can change it.
"No-one else can change it for us. We can't sit there moping around about it."
Cook has not completely given up hope of retaining the Ashes, knowing one win can turn the momentum and a drawn series is enough for England as the holders of the urn.
But he concedes it will take a 'monumental effort'.
"(Trailing) 2-0 is not a great situation to be in, but if you look at it like a football game, the next goal can change it very quickly.
"It (retaining the Ashes) is certainly not impossible. A lot of people sitting in this room and outside will probably give us no chance but if we believe in the dressing room that the urn is gone then it might as well be gone.
"If we don't believe it then no-one else is going to believe it.
"We've got to look right deep into our souls, into our hearts and turn it around ourselves.
"It's going to take a monumental effort to do it."
Making the task that much tougher still for the tourists is that the third Test starting this Friday is at the WACA, where England have a nightmare record across 12 Tests, with eight losses and only one victory – way back in 1978 before any of the current touring squad was born.
Cook believes England's long-time WA woes are immaterial.
"What's gone on in the past in Perth is of no relevance whatsoever," said the England skipper, who will celebrate his 100th Test in Western Australia.
"You can say we haven't won there for however many years, it's of total irrelevance to this team.
"We have to go there as this side in 2013 and deliver something very special otherwise we're not going to do what we came here to do."
As captain, Cook is fully aware of the need to improve his own output after the Australians had his number across seven Ashes Tests this year.
Cook has averaged 25.64 without a single ton in Ashes battles this year, including twin failures of three and one in Adelaide, falling victim to rampant Mitchell Johnson on both occasions.
"I need to score more runs, simple deal," Cook said. "There's only so many times you can tell the lads to do it if you're not delivering.
"I'm there at the top of the order as a batter and these last two games I haven't been scoring enough runs.
"There are some very tough moments as a captain and we're in the middle of it.
"We're 2-0 down and I'm responsible as the captain for that in the sense that I'm leading the troops out there.
"It does hit you quite hard."