The 62-year-old told his players on Saturday night, at their hotel in Charlotte, that he was bringing the curtain down on his seven-year reign after it was confirmed that the Scots had failed to progress from a group containing Brazil, Morocco and Haiti.
The shock announcement came exactly a month after he signed a new four-year contract that would have incorporated Euro 2028 and the 2030 World Cup.
In a Scottish Football Association interview reflecting on his time in charge, Clarke - heavily criticised in some quarters following back-to-back defeats by Morocco and Brazil - said he was leaving "just because that's the feel".
"What I wanted to make sure was that when I felt it was time to step away, it was time to step away," he said.
"Signing the contract before (the World Cup) was a case of trying to give a little bit of comfort to the players knowing that we could continue the journey.
"I always had in my head that if we didn't come out of the group, which is something that we've tried to do across three tournaments now ... that if that didn't happen then it was probably the right time to step away.
"Obviously if we'd managed to get that extra point and got out of the group then I'd probably have stayed on and tried to do another tournament."
Asked if it was an easy decision, a philosophical Clarke said: "Yeah, in some respects it was easy because I already had in my head what I wanted to achieve as a head coach. I'd also ticked all the boxes.
"I wanted to go to a major tournament with my country. I did that with the Euros. The first Euros (in 2021) was a little bit not the Euros because it was Covid affected.
"The second Euros was great. The tournament didn't go as we wanted but getting to Germany was fantastic. My lifelong ambition was to do a World Cup with my country. I've done that, so not a bad time to step aside."
Despite the backlash to Scotland's group-stage performance, Clarke is adamant he had a "brilliant" World Cup experience.
"I said I was going to enjoy it," he said. "Coming out for the Haiti game with the Scotland fans there in their thousands and my family in the stands was just the best moment.
"The next two games were tough. We played difficult opponents. Morocco and Brazil, both of them can go really deep in the tournament and we competed with them, no matter what other people might say. We competed, both games were competitive.
"We showed a lot of character and we played some good stuff."
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