Why the happiest? That defeat enabled the skilled, disciplined but very modest Finnish boxer to withdraw from the high-powered and highly-financed arena of world engagement and settle into the richer rewards of a simple life with his sweetie Raija.
That's all Olli ever wanted. He was fine with being European champ, but he's pushed into the world title match and burdened with the onus of Representing Finland by his windy manager Elis.
Elis hates Olli's modesty and simplicity. His ego demands Olli give him glory. His financial straits require he court rich backers and land a big time purse.
Elis's marginalizing of Raija drives her back to their "backwoods" (Elis's term) hometown, to Olli's frustration and loss of focus. Elis keeps Raija out of the photos and documentary film in order to sell a poster of Olli posing with the stiff and much taller (i.e., incongruously mismatched) Miss Finland.
The film is as much about Finland as about its historic boxing star. Olli is relieved to walk out of the formal post-fight banquet, preferring to skip stones with his Raija. Finland can similarly be satisfied with its own cultural and economic life, participating in Europe, but not feeling the need to take on the empty glitz of America and the world arena.
For such unnecessary aspiration is hubris, which In the fight was Olli's error: "I couldn't see him coming at me. I think I held my chin too high."
In its own modesty the film is shot in black and white, like the documentary we see being filmed, everything low-key and human. Its charm is simplicity and the poignant. Like the dedication on the couple's wedding rings: just the names and date. Like their engagement, outside the bus that takes Olli away, the couple standing apart and not even touching after her acceptance. It's even playful, as Raija's acceptance seems conditional upon him winning the fight — which we know is out of character for both.
Finally, a reminder why you should always read the full credits at the end.
In the last scene the young lovers pass an elderly couple holding hands. "Do you think we'll be like that?" Raija asks. "Old?" "No, happy." "Of course we will." The last credit identifies that elderly couple — whose faces we don't see — as the real Olli and Raija Maki. Their presence confirms this reading of Olli's happiest day.