Former British and Irish Lions full-back Rob Kearney said the current side will be "full of regret" after losing the deciding Test against South Africa.
"They started getting a bit sloppy in the last five to 10 minutes," he told BBC Radio 5 Live's Lions Verdict.
The defeat means world champions South Africa take the series 2-1.
Kearney's comments were echoed by his former Lions team-mate Shane Williams, who said the Lions were "in control" as they led 10-6 at the interval.
"Especially in the first half, you look at the territory and the possession the Lions had, there were definitely 14 points left out there," Williams told BBC Radio 5 Live.
"They were in control and played with tempo.
"But unfortunately in the second half, South Africa slowed the game down to a tempo that suited them, and it took about the 16th minute of the half until the Lions woke up."
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Marginal decisions cost Lions
Lions head coach Warren Gatland said some "50-50 calls probably didn't go our way" after South Africa went on to claim victory in the final minute.
With the game poised at 16-16, the Springboks were awarded a late penalty, which Herschel Jantjies decided to take quickly.
The replacement scrum-half was tackled and dispossessed of the ball on the ground, but play was brought back for the initial penalty as it was deemed Jantjies did not take it from the mark.
Steyn kicked the winning penalty, as he did in the series decider in 2009, and Gatland said it felt like "deja vu".
"You know it's not going to be easy going away and playing the world champions," said Gatland. "It could have gone any way and our congratulations go to South Africa.
"The penalty count was against us 15-12, and at this level it is so important. Your aim is to keep your penalties under 10 and if you can do that it makes a big difference.
"You get one or two chances at this level and you've got to make the most of it."
The bright note for the Lions was the performance of fly-half Finn Russell, who replaced the injured Dan Biggar in the 10th minute.
Russell had not featured in the Test series until this point but Gatland said the Scot was "excellent".
"We talked about moving the ball and the ball went through his [Russell's] hands a lot," said Gatland.
"He showed how quick he can get the ball through his hands. He created some stuff, and for someone who hasn't played a lot of rugby, I thought he was excellent."
Former Ireland full-back Kearney was also full of praise for Russell, while Williams, who toured with Kearney during the series defeat by South Africa in 2009, said he made "the world of difference".
"Finn Russell was superb and he brought pace and ambition," Kearney told BBC Radio 5 Live.
"We spoke about this side being braver and taking more risks, and we cannot in any way lament them for that."
It was Gatland's first series defeat as a Lions coach but the Kiwi was non-committal over whether he would return to lead the 2025 tour to Australia.
"In terms of my involvement, there's a lot of water under the bridge in four years. A lot of things can happen in that time. I've loved my time with the Lions," he said.
Nienaber hails 'fairytale' return of Steyn
South Africa coach Jacques Nienaber hailed Steyn's nerves of steel after the 37-year-old came off the bench to kick the winning points two minutes from the end of his first Test in five years.
"I'll be honest, I was sitting with my head between my legs, I didn't see the penalty," Nienaber said. "I'm happy for him in terms of having the opportunity to play again. It's a fairytale 12 years on."
Nienaber said Steyn's selection for the matchday squad of 23 was touch and go with Elton Jantjies having been the second-choice fly-half for the last few years.
"Morne's selection was an hour-long discussion from the coaches between the two players," he added. "But we felt his experience in this particular environment was the key."
And the coach praised the resilience of his players after most of the squad tested positive for coronavirus in a difficult build-up to the series.
"Our biggest challenge was getting time to prepare as we had some Covid-19 issues and had to sit in hotel rooms for a week," Nienaber added.
"Our attitude was to move on and find solutions. There was so much experience in the squad that we managed to get the work done in the end."
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