Stuart Lancaster admits Dylan Hartley's track record of imploding in pressure cooker matches was instrumental in his decision to remove the England hooker from his World Cup plans.
The Northampton captain was ruled out of the tournament opener against Fiji on September 18 and the trio of warm-up games preceding it after receiving a four-week suspension for head-butting Jamie George of Saracens in Saturday's Aviva Premiership semi-final.
Lancaster has reacted by dropping Hartley from his World Cup training squad and, in a twist of fate, replaced him with the player he assaulted at Franklin's Gardens, George.
England's head coach explained his thinking by highlighting the unacceptable dilemma posed by entering the World Cup with only two available hookers and referencing the difficulty in picking a player whose appalling disciplinary record now totals 54 weeks in bans for a range of offences including gouging and biting.
Every bit as important, however, is the worrying frequency with which Hartley has self-destructed when the stakes are high.
The unprovoked assault on George came two years after he was sent off for swearing at referee Wayne Barnes in the Premiership final at Twickenham, an act that ruled him out of the ensuing British and Irish Lions tour to Australia.
Lower on the scale of severity but adding more compelling evidence of a fragile temperament was the yellow card received for stamping against South Africa last November. A month later he was sent off for elbowing Leicester centre Matt Smith in the face in a fiery east midlands derby.
"Dylan has let himself down in this big semi-final and he has got to suffer the consequences," Lancaster said.
"Unfortunately the consequences aren't just for him, although they're huge for him, but also for the team because he was an important cog in the wheel.
"Dylan is excellent in an awful lot of ways but clearly emotional control and ability to make good decisions under pressure is a key quality in all players. And let's be fair, the white-hot pressure of a World Cup will be that."
Hartley is the second established England international ruled out of the World Cup for disciplinary reasons after Manu Tuilagi recently paid the price for assaulting a taxi driver and two female police officers.
Lancaster admits his most capped player, who pleaded guilty to the head-butt at Wednesday's hearing and chose not to appeal, had an inkling of what was coming when he informed him of his decision.
"Dylan was pretty disappointed, as you can imagine. He was pretty realistic as well, he understood what was coming," Lancaster said.
"In contrast to the Lions situation when he let himself down and missed out on an opportunity for himself, he feels he's let himself and his England team-mates down. That's probably cut him quite deep.
"You invest a lot of time and effort in a player, so losing one of our most experienced players at this point is hugely disappointing."
Lancaster stopped short of ending Hartley's England career, but admitted he would be "very disappointed" if he had to turn to him in the event of an injury crisis at hooker during the World Cup.
And when considering the options available to him when learning of the mindless attack, Lancaster knew there was only one course of action.
"None of these decisions are easy. It was an incredibly difficult position to be in and decision to make," Lancaster said.
"But when you weighed up the risk of going into a World Cup with only two hookers and the risk of losing another.....
"We're in the Fiji week and a physio comes up to me at the captain's run and says 'this hooker has a tight hamstring and can't play'.
"And I'm sat there as coach of the host nation playing in the biggest game we've had with one hooker and no one on the bench....people would look at me like I'm daft. That four-game ban was a game changer."
Hartley now enters familiar territory, forced to spend a summer reflecting on the short fuse that has damaged his career and reputation.
"I'm devastated with what has happened and the position I have put myself and the England team in," Hartley said in a statement released by the Rugby Football Union.
"I would like to apologise to Jamie, Stuart, and my team-mates both at Saints as well as England. What happened is not acceptable and I understand why this decision has been made."