The hike was never supposed to be considered that dangerous.
Initially a way for the assistant coach to learn to manage the young soccer players on his own, and a kind of team-building exercise for the Wild Boars, the seemingly innocent excursion quickly took a turn that's since captivated the world for two weeks.
For live coverage of today's rescue operation, click here
What started as a "rite of passage" for the 12 Thai schoolboys, aged between 11 and 16, was then described as a situation "worse than any horror movie you could imagine".
The adventure — one taken by several boys many times before — was said to be crucial to the team's training because they spend as many as 20 hours a week together.
The difference this time was the time of year — and the coming weather.
Many had never dared venture into the notorious Tham Luang cave system — Thailand's longest with a series of tunnels, slippery rocks and cliffs with stark drop-offs shrouded in darkness — during the country's wet season.
The large warning sign at the start should have been an indicator — it tells how the caves can rapidly flood during monsoon season.
While some locals and young boys say they are warned to stay away from the infamous and "off-limits" system at this time of year, others say they'd already gone several times and are always well prepared for their journey.
Read more: I was on the verge of panic the whole time
The young coach, Ekkapol "Aek" Chanthawong, was said to be keeping the boys on a strict training schedule and that often included biking across the hills that surround Mae Sai from their soccer field nestled by the mountain range.
Nopparat Kathawong, the 37-year-old head coach of the Wild Boars, told The Washington Post he didn't know where Ekkapol would be taking the team but he trusted them.
All he asked was that he take some of boys from the older team for extra eyes and for Ekkapol to ride his bike behind them to "keep a lookout".
On June 23, the group set out on their mission — a 45-minute bike ride from their school to the cave — without him because Nopparat had an appointment.
It wasn't until 7pm when he turned his phone back on that night that he realised something had gone terribly wrong.
Somewhere between the boys leaving their bicycles at the entrance to the cave, the sky opened up with heavy rain that filled the tunnels with water and cut off their exit route.
They had no choice but to keep forging ahead, along elevated slopes, where they found a dry ledge 4km into the cave that would ultimately make their rescue even more treacherous, leaving them stranded in total darkness for days.
All Nopparat found when he made it to the entrance of the cave that night were the boys' bikes and bags next to what triggered his worst fears — water pouring out from the opening.
"I screamed — 'Ek! Ek! Ek!' My body went completely cold," he told The Washington Post.
That triggered an international rescue operation and on July 2, more than a week after they went missing, two divers found the group alive, deep from the cave's entrance and huddled on a 10sq m ledge.
The painstaking rescue has so far seen eight boys safely out with four others and the coach still trapped.
The head of the rescue operation would not confirm whether all five could come out today, raising questions over whether Ekkapol could be left behind to spent a lonely night in the cave.
Boys who didn't go and know him have faith he will survive, despite reports he is the weakest of the group having sacrificed his food for them.
Two boys who go by the nickname Queue and Kaan didn't end up going on the hike but told the ABC they wouldn't hesitate following their coach into the system because they trusted him with their lives.
They said he would often give the boys a pep talk before going in, spending up to six hours inside with food, water and lots of flashlights.
But with Ekkapol having been a monk and teaching the boys how to meditate, even when their torches went out and they were surrounded by bats, they would never be scared.
The goal of the mission was to scrawl their names at the end of the 2.5km tunnel as proof they'd completed the journey.
Queue had never gone during the rainy season but said he had already been four times this year with their coach, trekking a few kilometres each time.
Boys by the names Puwadet and Kittichoke play on the same football team and might have been with them if they hadn't skipped practice.
The boys are never made to go on the extra training after practice and can get their parents to pick them up if they decide not to.
Others are hailing the trapped team as heroes, with 16-year-old Nanthawat Prangsangwilia, who nickname is Gan, saying they will be stronger when they come out
"When they come home, those kids will be able to teach us something — about how to survive, about how to stay safe in the caves," he told The Independent.
But Kittichoke Konkaew, a 14-year-old whose close friend, Nuttawut Takumsong, was in the cave said he had been worried something would happen to them when they defied local warnings.
"I was very worried about what would happen to them. The caves are a dark and scary place. I wouldn't dare to ever go in there," he said.
Co-ordinator of the National Cave Rescue Mission, Anmar Mirza, who has been involved in cave rescues for 30 years, told CBS, "You can't make a horror movie that would even compare."
Even for the boys who have so far made it out, the terrifying ordeal is far from over.
Their rescue, at least, may have helped the others left behind, according to Associate Professor Sarb Johal, from the Joint Centre for Disaster Research in New Zealand.
He said any feelings their situation may have become hopeless might have turned around.
"From the perspective of those boys and their coach, the relief of being found may coexist with the knowledge that they remain stuck and that their future remains uncertain," he said.
"Added on top of that may be the feelings of guilt that the coach may experience, even though it is clear that he has sacrificed his self-care to try to prioritise the wellbeing of the boys in his care."
But he said their physical circumstances also had the potential to cause harm.
"The lack of daylight over this period of time means that they may not only be psychologically disoriented, but that many of their basic physiological functions that depend upon circadian rhythms will be disturbed, such as sleep, hormonal functioning, core temperature, their feeding and drinking, and also how their gastrointestinal systems might be functioning," he said.
He said it was likely the divers and other members of the rescue teams would need care and support for their own wellbeing as this situation continued to unfold.
Water levels inside the cave are fluctuating, making it difficult to know for sure how long some of the final dives will take, or exactly how what turned out to be the worst excursion imaginable will ultimately end.
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