The 2017 NBA Finals is the seventh consecutive championship series in which LeBron James has appeared. It’s a herculean feat that hasn’t been accomplished in over 50 years.

But James has nothing on Danny Crawford. Crawford, one of the NBA’s all-time greatest referees, made his 23rd straight NBA Finals appearance in 2017’s game one, as the Golden State Warriors drubbed James’ Cleveland Cavaliers. Quartz crunched the data: It’s the longest streak on basketball’s biggest stage by a referee since 1975.

It’s not a matter of luck. Just as NBA teams are eliminated from the playoffs based on performance, so too are officials. After each round, the NBA reviews video to assess the accuracy of referees’s calls, and only the top performers move on. “The Finals is the pinnacle for our officials, just as it is for our teams, coaches and players,” said Byron Spruell, NBA President, League Operations, in a league statement. “Earning this opportunity is a testament to each official’s work ethic and unwavering commitment to their profession.”

Every one of the NBA’s 64 full-time referees has earned a rarefied designation. There are hundreds of thousands of referees across the world, and very few could make it through the NBA’s officiating wringer.

The NBA identifies potential refs through national tryouts and by scouting lower levels of officiating, like high school and international leagues. Once a candidate is selected, they go through a long process of training, attempting to climb the ladder from the NBA’s developmental leagues to primetime. Most never make it to the NBA.

NBA referees, who take flack from fans and players alike, are generally quite accurate. The NBA released an assessment over 1,700 decisions made by referees, and found that they got it right 86% of the time. The biggest problem for referees is being gun shy—when they do choose to “blow the whistle,” they were found to get the call right 97% of the time. ”Everybody thinks they can do our job, but very few can,” said veteran referee James Capers in a recent interview. “Referees in the NBA are very good at what they do.”

All NBA referees may be good. Crawford is special. The NBA’s analysis of specific referee’s performance are not public, but in addition to his finals streak, Crawford’s greatness is confirmed by how he is viewed by players and coaches across the league. In an anonymous poll of 36 players and coaches conducted by the Los Angeles Times, Crawford was listed among the three best referees in the league by 30 of the respondents—more than any other official. (The man in second, Joey Crawford, is no relation.)

In addition to his excellence in calling games, Crawford is also lauded for his communication skills. ”Danny is good because he’ll talk to you,” one player told the Times. “If you’re asking a question, even if you’re questioning his call, he doesn’t take it like it’s an affront to his manhood.” As one of the best who to ever do his job, Crawford has every reason to feel comfortable with a little criticism.