So, for the third straight season, the Warriors and the Cavaliers are facing off in the N.B.A. finals.

Though many saw this matchup as inevitable, it’s a historical anomaly. While there have been dynasties before in the N.B.A., it’s rare for two of them to line up so closely. The finals have never before matched the same teams three years in a row. Injuries, aging, loss of form and sheer randomness always seemed to get in the way.

Even in the dominant Celtics-Lakers eras, the same teams never met in the finals three times in a row. The Celtics reached 10 straight finals in the ’50s and ’60s (winning nine of them). Nine of those were against the St. Louis Hawks or the Minneapolis/Los Angeles Lakers. But never three consecutively.