He was armed with only knives and aware that he'd face serious punishment -- or perhaps even be shot, if his identity was mistaken as he approached the outpost -- if he turned back.
"I'm going, 'Good grief, I'm in over my head,'" Bergdahl said in a "Serial" podcast released on Thursday.
"Suddenly, it really starts to sink in that I really did something bad. Or, not bad, but I really did something serious," he said.
So he set off to gather intelligence and mimic a film idol: Jason Bourne.
He decided to collect intelligence on the Taliban in hopes it would help him eventually return to the U.S. military with something to show for his absence.
"Doing what I did is me saying that I am like, I don't know, Jason Bourne," Bergdahl told Mark Boal, the filmmaker whose interviews with the Army private first class will make up the second season of "Serial."
"I had this fantastic idea that I was going to prove to the world that I was the real thing," Bergdahl said. "You know, that I could be what it is that all those guys out there that go to the movies and watch those movies -- they all want to be that -- but I wanted to prove I was that."
It didn't work. Bergdahl, armed only with a knife, said he was quickly captured by Taliban fighters on motorcycles, starting what would be nearly five years in captivity -- ended only when President Barack Obama swapped five Taliban detainees who had been held at the Guantanamo Bay detention facility for Bergdahl's freedom in May 2014.
Bergdahl could now face a court martial and charges that could lead to a sentence of life in prison. He's assigned to an administrative Army job in San Antonio.
Boal, a filmmaker who wrote and produced "The Hurt Locker" and "Zero Dark Thirty," conducted 25 hours of interviews with Bergdahl. The podcast's creator, Sarah Koenig, said its second season will focus largely on those interviews.
Here are four other interesting tidbits from the first episode, titled "DUSTWUN" -- or "duty status -- whereabouts unknown."
-- Bergdahl said he was rebelling against "leadership failures" at his outpost and hoped his departure would provoke investigations by creating a crisis. Bergdahl said he feared "the lives of the guys standing next to me were in danger of something seriously going wrong."
-- He quickly realized he couldn't fight off the Taliban. A line of about five motorcycles with Taliban members riding on them found him as he walked along a road in the open desert, and six or seven riders were armed with AK-47s. "All I had was a knife. I'm not stupid enough to try knife off a bunch of guys with AK-47s," he said.
-- He was held in grim conditions by the Taliban. He said "standing in an empty, dark room hurts -- physically, but more than that. It's mental. You're almost confused," he said, adding that he would wake up in the dark unable to see his own hands.
-- Bergdahl pushed back against claims from other soldiers that he'd left a note behind expressing his disillusionment, saying he'd left no such note. It signaled that he could oppose some elements of the version of events from his departure made public so far.