One does not simply play both rugby sevens and 15-a-side rugby.
They may share a pitch and similar rules, but the demands are different, and few players can say they have thrived in both rugby union variants.
Sonny Bill Williams is one and he is the headline name within the list of Rio 2016 participants going into this year’s Rugby World Cup.
But he is not one of the eight players heading to Japan with an Olympic medal in his possession.
Four of those came from Fiji's gold-medal winning team with the cousin of 400m world-record holder Wayde van Niekerk also standing on the podium.
Appropriately enough, there are a total of 15 players from Rio in the squads in Japan. Find out who they are:
The many talents of Sonny Bill
Versatility is embedded in Sonny Bill Williams’ DNA.
The New Zealander first crossed codes from rugby league to union in 2010, by which point he was already a professional boxer.
In the ring he won international and New Zealand heavyweight titles, while on the pitch he has won the last two World Cups with the All Blacks.
Naturally, Williams took to sevens comfortably when switching ahead of the 2016 Games, but his Olympic adventure ended early when suffering an injury in the opening game against Japan.
New Zealand went on to finish fifth in Rio, and Williams’ focus is now back on 15s and a third World Cup win.
He will be joined in his quest by fellow sevens Olympian and Auckland Blues team-mate Rieko Ioane.
One of the fastest players in the world, Ioane averages almost a try every match for the All Blacks.
The 22-year-old will want to maintain that form as New Zealand look to go the distance once more.
Despite having a population of under a million, Fiji are powerhouses in the world of rugby sevens.
Since the World Sevens Series began in 1999, Fiji have finished in the top four every season, winning the title four times.
Victory in 2015 and 2016 saw them head to Rio 2016 as favourites for the gold.
And they delivered when beating Great Britain 43-7 in the final for the nation’s first Olympic medal of any colour.
The quartet’s next mission will be to exceed Fiji’s best finish at a Rugby World Cup, where they have twice reached the quarter-finals in 1987 and 2007.
Speed runs in the family
World record breaker Wayde van Niekerk was not the only medallist within his extended family at Rio 2016.
Speed is clearly a family trait, and Kolbe’s pace and incredible step eventually earned him a call-up to South Africa’s 15s side in 2018.
The Toulouse fullback will be heading to the World Cup alongside fellow bronze medallist Kwagga Smith, who also made his Springboks debut last year.
McConnochie’s rapid rise
As meteoric rises go, few can match Ruaridh McConnochie’s story in world rugby.
McConnochie was originally a reserve for Great Britain's Olympic sevens team in 2016, but injury saw him bumped up to their 12-man squad.
He soon had a silver medal to his name, and two years later he signed his first contract with a top-flight 15s side when joining Bath.
But McConnochie’s remarkable journey up the rugby ladder did not stop there.
He went on to make his England 15s debut in September, and is set to cap his fairytale story at the World Cup.
James Davies also won silver with GB in Rio, but he will not be donning the same jersey as McConnochie in Japan.
The Scarlet flanker is in Wales’ squad after making his international 15s debut in 2018.
Along with McConnochie and Davies, there are two more players who stand as the sole Rio 2016 participants in their respective World Cup squads.
No place like home
Japan were the surprise package of the last Rugby World Cup in 2015, beating South Africa's mighty Springboks 34-32 in the group stages.
The sevens team also sprung a huge surprise Rio 2016, defeating New Zealand in their Pool C opener and going on to reach the semi-finals.
Defeats to Fiji and then South Africa in the bronze-medal playoff saw Japan miss out on hardware, but those two wins against the odds will inspire them heading into this Rugby World Cup and Tokyo 2020 with both events taking place on home soil.
And the Sunwolves trio will hope for a similar run on home soil as Japan seek to surpass the pool stages for the very first time.