England were trailing 16-12 at Twickenham on Saturday with just over a minute remaining when Robshaw, after some apparent on-field indecision, instructed Owen Farrell to kick the goal rather than go for the corner.
Last weekend, Robshaw was criticised for not taking the points on offer as England slipped to a 20-14 defeat to Australia.
Robshaw denied that experience had influenced his decision, explaining that he felt England still had time to kick the penalty and then get back down field.
But England failed to gather the restart and South Africa saw out the closing seconds to complete a 16-15 win and extend their unbeaten record in the fixture to 11 matches.
"All those decisions comes down to me," Robshaw said.
"I thought we had the time to get the points and get back down there.
"We always look back at decisions. It was one of those where if we had won it would have been the right decision. Unfortunately we were on the wrong side of the result today.
"We will go back and look at the video and analyse it."
Robshaw went for the posts despite some of his team-mates on the field believing the decision would have been to go for the lineout in an attempt to score the match-winning try.
The counter-argument is that England's lineout, in wet and greasy conditions against the well-drilled Springboks, was not as reliable as it had been against Fiji and Australia.
"We discussed it and I have to make those calls at the end of the day, that is on me and I thought we still had time to get the points, get back down there with the re-start and put ourselves potentially in drop goal or penalty range," Robshaw said.
"I am the one who makes that call. It is on me.
"People have to make their own decisions. You have to read the game the way it's going, how you feel you can get the best out of it."
After the game, Farrell said that he backed Robshaw's decision.
"It wasn't my decision. Not that it was completely on his shoulders. We were always going to back his decision because he is the captain and makes the calls," Farrell said.
"We still thought we would win the game.
"We have played very well today, I thought. I thought we played a lot of good stuff.
"We thought we controlled most of the game. We were unlucky because their try was a freak, you don't see many scored like that.
"The heart the boys showed, the will to win, the will to put their bodies on the line - when it is time to get stuck in, it is time to get stuck in and I think we did that unbelievably well today."
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