The origins of the kahs-wan originate from the ancient Vulcan warrior days. When the Vulcans turned to logic, they reasoned that they must maintain the tests of courage and strength to keep pure logic from making them weak and helpless. For a Vulcan, to fail the kahs-wan once is not considered a disgrace.
Spock was scheduled to face the kahs-wan ordeal on the 20th day of the month of Tasmeen in the Vulcan year of 8877 (Earth year 2237). However, he decided to take the trial early and his sehlat, I-Chaya, insisted on accompanying him and died trying to fight off a le-matya. (TAS: "Yesteryear")