Armstrong had trained every day since with a specific day in mind — the day he'd step into the throwing circle in London and with huge toss, finally erase the heartbreak of the 2008 Beijing Games.
The London Olympics, however, ended in more heartbreak for Canada's finest thrower.
The 31-year-old from Kamloops, B.C., who was ranked No. 1 in the world last year, threw 20.93 metres to finish fifth in Friday's shot put final.
"At least it wasn't by a centimetre this time, if you want to look at it that way," Armstrong said with a half-hearted laugh. "But I'm going to keep my head up and just go hard next year and see what happens there, and hopefully try to get a gold at the world championships. You've got to move ahead, this is a tough sport."
Tomasz Majewski of Poland threw 21.89 for gold while Germany's David Storl won silver with a throw of 21.86. American Reese Hoffa took bronze with 21.23.
Heptathlete Jessica Zelinka of London, Ont., meanwhile, made a spectacular comeback, roaring up the standings from 19th place earlier in the day to third overall heading into Saturday's final events.
Armstrong, however, was the one considered Canada's top hope for a track and field medal in London. He was the most consistent thrower on the planet last year at this time, and his Canadian record toss of 22.21 stood up as the best in the world.
Between then and now though, Athletics Canada head coach Alex Gardiner believes perhaps the medal hopeful label began to weigh heavily — too much even for the broad shoulders of the beefy six-foot-four, 345-pound mountain of a man.
"Dylan's a pretty easygoing guy. I don't know how the subconscious works. He had a lot of hopes riding on him," Gardiner said. "He had sponsors, he had family, he had the whole city of Kamloops. I don't know what that does to you but it's got to do something.
"If you think you're carrying that kind of responsibility. . . maybe he needed to think about caring more about himself but he's not that kind of a guy. He's not a selfish man at all."
Armstrong hasn't had the season he had last year, hampered by an elbow injury in the winter that sidelined him for several weeks. His best throw this season was 21.50, eighth in the world — a distance Gardiner said he probably tossed 20 times last year.
Gardiner sensed Armstrong wasn't himself Friday in front of a jam-packed crowd of nearly 80,000 fans at Olympic Stadium. His mom and his younger brother David cheered him on from the crowd, David clad in an outfit that looked like a couple of Canadian flags sewn together.
But the veteran thrower, silver medallist at last summer's world championships, was uncharacteristically nervous in the morning's qualifying round that saw him squeak into the final on his final throw.
"I thought it was flat. It wasn't inspired," Gardiner said. "I didn't see what I had seen before, certainly at nationals and at worlds. I think he knows he was flat tonight. I didn't see the pop in the circle.
"There was definitely something missing. I felt there was a missing piece there and I don't know what it is."
Armstrong's personal coach Anatoliy Bondarchuk sensed something was up too.
"I know Anatoliy was a little concerned," Gardiner said. "I asked him how things were and he said 'OK.' He usually says 'Good.' I'm sure Anatoliy thought he could throw 21.30 or 21.50 as well."
Gardiner said Armstrong will be keen for redemption.
"He won't be happy with this," the coach said. "He'll have some time that will be a little more emotional than what he displayed here tonight."
Armstrong kept his emotions fully in check as he spoke to about a dozen Canadian journalists, and he insisted he would remain stoic after he left the stadium.
"The same," he insisted. "Fourth and fifth at the Olympics, I can deal with that, at the end of the day I can deal with that."
Asked if he'd wash down his disappointment with ale or lager, Armstrong laughed and said "Guinness."
Armstrong, who turned down a dozen or so NCAA scholarship offers for football to focus on track and field, said he's not ruling out the 2016 Olympics. But he'll be 35 years old competing in a power sport, and as Gardiner pointed out, testosterone in males drops off significantly at that age.
His short-term plans include getting a bone chip surgically removed from his right elbow in September.
"That affected (training) quite a bit, I'm not going to lie, taking almost a month off and then nursing it for another three weeks after," Armstrong said.
Meanwhile, in the heptathlon, Zelinka is making up ground after a disastrous high jump that left her well back in 19th place.
Zelinka got off to a strong start a personal best of 12.65 seconds in the 100-metre hurdles that put her second. The 30-year-old plummeted to 19th after the high jump.
"I could have a lot of excuses if I want. I still haven't figured out the stupid event," Zelinka said. "At this point, I've been pretending I love it — 'Oh, I love you high jump. We're friends, we're friends' — and now I don't need to be its friend anymore. Screw it. It screwed me over too many times."
Zelinka cleared just 1.68 metres in the high jump — well off her best of 1.79. She climbed back up to 10th with a toss of 14.81 metres in the shot put, the third event of the day, then ran a personal-best time of 23.32 seconds in the 200 metres to rocket up to third in the standings.
"After the disappointment, I'm going to sulk, and sulk some more and sulk some more and then I'll come back to the track and be ready to get back in it," Zelinka said. "It made me even more determined because I'm not leaving these Olympic Games being disappointed just by one (poor) event."
British star Jessica Ennis leads the overall standings with 4158 points while Austra Skujyte of Lithunia is second at 3974 and Zelinka has 3903.
Brianne Theisen of Humboldt, Sask., is 15th with 3763.
The event wraps up Saturday with the long jump, javelin and 800 metres.
Also on HuffPost