Coming from nowhere to stand on the World Cup winners' stage with the 2019 champion South Africans, Jantjies, 23, (pictured) defied the odds.
During the 2018 season, Jantjies made his mark with Western Province in Currie Cup rugby and that resulted in his inclusion in the Stormers for the 2019 Investec Super Rugby campaign.
He was soon pushing potential Springbok rivals Embrose Papier and Ivan van Zyl into the background through the quality of his performances.
That was reflected when Jantjies made his Test debut in July, celebrating the occasion by scoring two tries to help beat Australia.
New Zealanders then experienced the Jantjies phenomenon for themselves a week later when he came onto Wellington Stadium as a substitute to score the try that allowed South Africa to draw the Test.
Just how quickly it all happened for him was summed up by Springbok lock, and Stormers teammate, Eben Etzebeth ahead of the World Cup.
"I asked him where he was at this time last year? He was in the Currie Cup mix, and occasionally limited to a role on the bench. I said, 'Did you ever think that in a year's time you would be starting for the Springboks and you would be in line for a World Cup place?' He said no," Etezebeth told sarugbymag.co.za.
An influence on Jantjies at the University of Western Cape in Cape Town was the late Springbok wing Chester Williams who helped him to success in the club competition in 2018.
Williams, who died in 2019, did see Jantjies make his Test debut and said not long before his death that Jantjies was a very mature person in spite of his age.
"The boy has a massive heart and a will to succeed. That is something you can't coach. That comes from the heart. The desire to be the best you can be," he said.
Another early influence, a teacher at his primary school, Christo Jephtas, said, "The first time I saw him he had a rugby ball in his hands while we were training for athletics.
"He was passing and kicking the ball. He was stronger and quicker than the other kids in his group. He was very disciplined. At age 10 he was like somebody who had a world's experience. He knew what he wanted from life," he said.
Another who helped Jantjies was the former Springbok halfback Bolla Conradie, who developed his positional and defensive play at his university club.
"He was always the first guy on the field and showed a lot of leadership qualities. He put in the extra effort and hours to be where he is now," he said.
"He is the type of player who sums up the situation well and his passing and clearing are always good. He can tackle loose forwards. He is not scared to make contact and he plays with a lot of heart."
Jantjies didn't over-complicate things either, Conradies said.
"A lot of scrumhalves have a good pass or a good kicking game, but Herschel has got both – and vision. But it all starts with him doing his primary job really well, which is getting to the breakdown and executing well," he said.
Jantjies credited Springboks teammates and halfbacks Faf de Klerk and Cobus Reinach for working with him and he never thought about his lack of size compared with the players around him.
"I try to go in with everything. I play out of my heart, so my body shape or type will never matter to me.
"To the smaller guys, they must just enjoy the rugby and put everything into it. If you are going to be scared and think about injuries, eventually you are going to get injuries. Or, if you think about a guy running over you, he will eventually run over you," he said.
"It's rugby, it's physical. You can't shy away from the physical stuff. You've just go to climb in there and embrace it," he said.
The final word on Jantjies' future lay with Conradie.
"He's going to be a superstar. Scrumhalves don't really come into their own in terms of decision-making until their late twenties. He is already mature and can only get better. That is the scary part.
"We don't have to worry about him getting a big head, because he knows he has to keep working hard to be successful. I'm just looking forward to seeing how he grows as a player and a person," he said.