The visitors shut down him down with their rush defence. The Lions got in his space, reduced his time on the ball and collectively the All Blacks didn't have either the skill execution of strategy to play their way out of trouble.
Barrett, therefore, was never able to stamp his authority on proceedings and the All Blacks, without their tactical director on the bridge as prominently as they would have liked, struggled to be in the right places and do the right things.
There was considerable disappointment within the All Blacks that they didn't find solutions to their problems during the series and Barrett unquestionably feels much of the responsibility for that failing.
"We were perhaps tested in areas where we haven't been before so that's exactly what we wanted," he said. "We ask those hard questions of ourselves and of our teammates and it gets the best out of the team. It is just what we needed.
"Some teams in Super Rugby adopt that style of defence too and we do understand that it puts the person with the ball under a bit more pressure, but there are opportunities elsewhere so if the Wallabies do bring that on Saturday we have learned ways to deal with that."
He says that with an intensity that gives away how much he wants to use the opening Bledisloe Cup clash to prove what he has taken on board. It's one thing to be talking about what has been learned, but it is emphatic and considerably more compelling to actually prove it with a definitive and commanding performance.
He feels much the same way about his goal-kicking, which was immaculate in the first test against the Lions and then patchy in the second and third. He can't go back in time to land those missed goals, but he can answer his critics in six days by improving his accuracy.
"There can only be one kicker mate and he's not here," Barrett said when asked whether the absence of younger brother Jordie puts added pressure on him.
"I have been goal kicking since I was six years old so I have always been analysing my technique and it is no different to any other skill set. I am excited about working hard on various areas of my game and excited by this weekend."
What's also driving Barrett's excitement is the opportunity to drive a big statement performance against the Wallabies.
However much Australian rugby may have its troubles at the moment, no one in the All Blacks is silly enough to believe they will face anything other than a highly motivated, well-drilled Wallabies team on Saturday.
An no one within the All Blacks has lost any of their enthusiasm for the rivalry. Barrett confirmed that he still can't shake the memory of John Eales landing that last-minute penalty in 2000 and that behind the World Cup, the Bledisloe is the trophy the All Blacks covet the most.