And Williams knows there would be no better time to start addressing matters than next Sunday's World Cup Pool D opener.
Williams, Wales' record tryscorer, has never been part of a victorious Wales team against the Springboks, despite eight attempts during his 81-cap Test career.
Wales lost the last three encounters - all in Cardiff - by a combined aggregate of 12 points, and 34-year-old wing Williams has had enough of finishing second.
"South Africa are a side the last three times we've played them we have gone very close," he said.
"But we are fed up of going close. Hopefully, this will be the stage to beat them for once.
"It is a cup competition, and we know what we've got to do. We can't wait for the first game now.
"We have prepared very well for this World Cup. The guys are looking physically fitter than they've ever been, and a little bit more mentally tough than we were in the last World Cup.
"But all that doesn't matter if you don't perform on the day. We are making sure we are 100% prepared for this massive South Africa game.
"The feeling in the camp is great, and it's good to be part of, but it is all about doing it on the field as well.
"It suits us that we've got South Africa first. It will test both sides to see where we are and how far we've come over the last couple of months."
Wales' last World Cup journey reached a grinding halt in Nantes four years ago.
A 38-34 loss to Fiji - the Pacific islanders are back on Wales' World Cup agenda next month - meant Williams and company were sent packing with indecent haste, exiting before the quarter-finals.
Williams scored one of his 54 Wales tries that day in what was hailed as the tournament's most memorable game.
But he added: "I certainly don't want what happened in 2007 happening again - that defeat was one of the worst days in my rugby career, to be honest.
"With the World Cup, one mistake and you could be out.
"Every game in this group is going to be tough, but we have prepared well, and the atmosphere in New Zealand is hotting up.
"I went for a coffee last night, and you can certainly sense the nerves and excitement in the air."
Williams has consistently said he will retire from international rugby whenever Wales' latest World Cup adventure ends.
He is, though, still in prime form and likely to be among the first names on Wales coach Warren Gatland's list ahead of his team announcement next Friday.
"I am still enjoying my rugby," said Williams, who made his Test debut more than 11 years ago.
"I would like to think I am still playing well enough to be selected. Warren has still got his faith in me.
"Last season was a tough one for me. I was injured for the majority of it, but I have come back and made sure I trained hard enough to be fit for this World Cup."
That regime included two punishing summer training camps with the Wales squad in Poland, and he admitted: "That was very difficult.
"I had just come back from an injury, so I felt myself blowing in the first week of training out there.
"But it has given us a physical zip. We felt the fresher team in the three games against England and Argentina last month, so the Poland trips were a massive benefit for us. Hopefully, that will show against South Africa next Sunday.
"I have no doubt that if I am playing, South Africa are going to use the height advantage against me (Williams is diminutive by Test standards at 5ft 7in), but to be honest, I get that every other week.
"They do tend to kick the ball quite a lot, and we've got to make sure we are prepared to counter that. Hopefully, we will have a few tricks up our sleeves as well."
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