Edwards says biggest games are all played in the head

Wales call him a defence coach. At Wasps the job title is head coach. The two could be combined because if there is one thing Shaun Edwards can talk about with compelling sense, it is the defence of what goes on in a rugby player's head. "In the end you've just got to convince yourself you've got the bottle to do it," says the greatest multi-medallist across both codes. "Tell yourself you're a big-game player. Somebody else can say something to you but you've got to convince yourself. To the layman you could describe it as like going into an exam – though it's a slightly more physical activity."

That comment comes with a typical Edwards guffaw; a rasping and infectious laugh that, with his cueball-crowned game-face frown, is as familiar in union now as the short blond curls were in league when he climbed Wembley's steps nine times to collect the Challenge Cup.

But the serious subject at hand is growing evidence that Welsh players lack that bottle. Slip-ups in tight spots have been costly. A knock-on at a scrum and a lost line-out against South Africa in 2008; throwing away a lead against the same opponents last June; in the 2010 Six Nations' Championship, Alun-Wyn Jones's yellow-card trip against England, Lee Byrne's daft sin-bin in Ireland, and two missed kicks to touch during a fightback against France; a few months later, Byrne's penalty touch-finder off target versus New Zealand, and Ryan Jones conceding a penalty to hand Fiji a draw.

"Those are the things we need to eradicate from our game," Warren Gatland, Edwards's boss with Wales, said after the New Zealand match and he has tried rage and reason to put it right. At regional level Wales's Heineken Cup campaign collapsed with a groan last weekend when Scarlets kicked a penalty dead while leading against Leicester, and Ospreys' pack went two ways off a scrum when they had London Irish on the rack.

"It's impossible to replicate those specific, big moments in training," says Edwards. "Obviously the more you practise the skill, the better. But experience counts – particularly if not all those experiences have been bad. If they're all mistakes, it will get in your head a bit."

The Wasps side of a few years back had players of utter conviction: Lawrence Dallaglio, Josh Lewsey, Alex King. Do Wales have enough of them, given the incumbent captain, Matthew Rees, has been known to wobble at the line-out? "Well there's a lot of people in the team who have got two Grand Slam wins [2005 and 2008]," Edwards says. "What other team can say that besides France? They must have a certain mental strength."

So perhaps it's the coaching that is lacking when a throw that seems a straightforward skill goes astray? "The line-out is the most complex part of the game by a considerable margin," he says. "The most analysis goes into it, the most studying of the opposition, the skill of calling to the right place, the speed of the lift. Everyone blames the hooker, which often is wrong. The team plays a huge factor. Matthew did a good job as captain [in the autumn], he's got everyone's respect and he's an obvious starter.

"It's not just line-outs. It's missing that last-ditch tackle, or giving away a crucial penalty. And they could come at any time. I was proud of Wales's defence in the 2008 Grand Slam but the goal-kicking was 100 per cent going into the final match – a huge part of us winning it. Rugby is a game of momentum. The momentum-shifting incident could be at any time." As proved by the thrilling stoppage-time tries to defeat Scotland last year.

When Edwards was Wigan's full-back he went to a hypnotherapist to stop getting "over-aroused" before a match. It improved him by "two or three per cent". Now Andy McCann, a sports psychologist schooled in martial arts, is available to the Wales players. "He is unobtrusive. He understands the minds of those who play a high-contact sport."

By his own high standards, Edwards is enduring a lean spell trophy-wise, going back to Wasps' Premiership title and the Slam in 2008, his first as Wales's assistant coach. Defeat in Glasgow last Sunday was a heavy blow to Wasps' bid to make the Heineken Cup quarter-finals: they finish the pool at home to Toulouse today.

Wales have half a dozen first-choice players and a couple of back-ups injured. Edwards, who wants to coach a second Lions tour in Australia in 2013, makes no promises. "The way Gats has gone about it [with Wales] is like a boxer. You can go through an easy route, and get a record of 21 and 0, then come up short in the big fight. Or you can go the hard way, take a few losses on the way and when it comes to your big chance – which is obviously Rugby World Cup – you're more prepared. In the end we're all judged on Rugby World Cup, aren't we? If we get everyone fit and available, we're in with a chance.

"I'm not saying I'm pessimistic about the Six Nations. There'll be 15 lads playing for Wales against England in a fortnight who'll be bursting with pride. But we need a full-strength team to select from and unfortunately it's hit us again. I don't expect anyone to feel sorry for us, except maybe my mum and my grandma, so it's a matter of working with the lads we've got."