Others don't: chalk and cheese, water and oil . . . and Colin Hawke and Otago rugby.
Retired referee Hawke, who was famously blacklisted by Otago fans after the 1994 Ranfurly Shield challenge and the 1995 NPC final, was unexpectedly the centre of officiating attention again on Saturday.
Whistled in as a replacement television match official (TMO) for the Super 14 game at Carisbrook, Hawke made a late decision that Highlanders winger Fetu'u Vainikolo had not scored in the corner with five minutes to go.
If Vainikolo's try had been awarded and Israel Dagg's conversion had gone over, the score would have been locked up at 23-23.
But Hawke ruled Vainikolo was out while trying to score the try, the Sharks scored two minutes later, and it was game over.
Highlanders coach Glenn Moore was diplomatic after the game, saying he wanted to have another look at the incident, but Highlanders captain Jimmy Cowan said it looked like a try from where he was standing.
That Hawke got to make the decision came down to an illness 360km up the road, and a lack of available people to be the TMO.
Southland referee Keith Brown was set to referee the match between the Lions and Crusaders in Christchurch but was violently ill on Friday night and had to pull out.
That led to Garratt Williamson, who was going to be the assistant referee at Carisbrook, having to go to Christchurch to replace Brown.
Glenn Newman moved from TMO duties to replace Williamson, leaving a scramble to find a TMO.
If Brown had recovered he would have done the TMO job but he was still unwell.
Sanzar acting referee manager Lyndon Bray said he had no hesitation putting the experienced Hawke in the role.
"We are part of a team, with good people among that team, and Colin is one of them. He is the high performance referee coach so he's sort of the Graham Henry of refereeing," Bray said.
There was also doubt over whether Sharks hooker Bismarck du Plessis scored a try in the first half, after referee Jonathon White asked Hawke if there was any reason he could not award the try.
Hawke retired from active refereeing in 2002, but is still heavily involved helping and assessing referees.
Bray said Hawke got both decisions right.
"I think there is no doubt in the cold light of day that he [Vainikolo] is out. That was 100% a good decision."
Bray said for du Plessis' try, White could see a grounding and needed to know from Hawke whether there was any reason it could not be awarded.
Bray said the TMO role had a defined protocol and only qualified people could do it.
It was not simply a case of just looking at a television and making a decision or two.
Bray said he could have spent two to three hours schooling up a local referee on the job and going through all the protocol and processes but that would have been unfair to put someone under so much pressure.
The situation was not helped by top New Zealand referees Bryce Lawrence, Vinny Munro and Chris Pollock being out of the country.
