Imagine occupying a boat with the same person for days and days and weeks and weeks across 13 years, through two-man Olympic events and European championships and world championships, through Volvo Ocean Races and, as if that's just not enough, circumnavigating the world with just this one other person, with no stops or external assistance.
It would be a good idea to actually like that person.
"No, I like him a lot," Iker Martinez said.
"He's a good guy," Xabi Fernandez said.
Such a relief.
"Xabi, he's someone very special, no?" Martinez said.
It would be so demoralising to think they bickered constantly or hurled projectiles occasionally.
It adds a dollop of faith in a turbulent humanity that Telefonica's 34-year-old skipper (Martinez) and Telefonica's 35-year-old trimmer (Fernandez) dovetail almost magically.
After their Athens Olympic gold medal in 2004 and their Beijing silver in 2008 and their 49er world championships and their 95 days at sea together in the Barcelona World Race, you would have to call them one of sport's more becoming teams of any roster size.
"It's not very usual," Fernandez said charmingly.
Even among the world's abundance of close friends, it's not very usual that two would meet as tykes sailing in Spain's Basque Country at age seven or eight (neither remember just when) ... that one (Fernandez) would be in on the discussion with the other (Martinez) and his fiancee about when the latter should get married relative to the Beijing Olympics ... that two of their collective four children (two each) would arrive two days apart ... and that out in the lonely middle of the world's oceans in 2010 you would find these two guys, alone.
As their tandem of a big build (Fernandez) and a small build (Martinez) mingles into a crew of 11 on a Telefonica boat that leads the 2011/12 Volvo Ocean Race after two legs, the suspicion would be that these two personalities must vary.
The reality would be that these two personalities do vary.
Or, as Martinez quips: "I would never sail with myself, no."
"We are, I think, completely different," Fernandez said. "I think he's the natural skipper. He's pushing very, very hard, always, and I think I'm the other part, more calm and pushing back a little bit sometimes.
"He's got the ideas, always like crazy ideas, stupid, and then after a little time you realise he was right."
Martinez ladles credit on Fernandez.
"I think Xabi, most times, is more relaxed, he's more quiet; he always tries to spend a little bit more time to make the big decisions," the skipper said.
"I think that's helping us a lot ... I think what is helping us not fight is that Xabi's more quiet and more reserved.
"I think that's helping us to not get angry. I think that's coming a lot from Xabi's point of view, which is always more relaxed and trying to think two times before making a decision."
"Never," Fernandez said. "Sometimes we have stress, of course."
Continuing: "A lot of people who started with us, they split in four years, five years, and they are angry.
"We don't want this. I know him and he knows me. So sometimes we've got maybe some things we don't like, but we know it's temporary."
As for the timeless question of what on earth two guys discuss alone at sea for 95 days, Martinez said: "Most of the times they are not conversations. It's just to transmit information.
"Most of the times it's just for communication, just like, 'This is like this, this is what happened.' 'Good, I got it.' 'I go to sleeping and we talk later.'"
And for another distinctive chapter in the voluminous vagaries of human interaction, Fernandez said: "I have to say 95 days didn't get too long."
And then for yet another chapter, take this two-man bond and fling it into an 11-man crew, and its relevance neither diminishes nor detracts.
In fact, it helps.
Especially with a young skipper, Fernandez said. "I think my role is to make people understand what he's thinking, or why, or which way to make people understand his thinking. I really think he goes forward" with his thinking, "so I think sometimes he has some ideas and they're, like, crazy, and I think of my jobs is to make people understand."
Soon after Fernandez said that at the Telefonica base camp, I happened to walk past Martinez, half of a tandem that might not mesh were either even a tad different from how he is.
"He likes you," I said.
"Good," he said.