Warning: Contains spoilers for Squid Game.
The final confrontation between Seong Gi-hun and Oh Il-nam is the climax of Squid Game season 1 - but what does the final game the pair play really mean? In a show based on the idea of people turning on one another to win a series of children's games made deadly in order to win money, Gi-hun and Oh managed to be some of the most endearing figures of the Squid Game cast. Oh - an old man who appeared to be struggling with memory problems as a result of a brain tumor - took a whimsical joy in the game that seemed to make it clear to viewers that he didn't understand the gravity of the situation, making him an immediately sympathetic figure. The main protagonist of the series, Seong, similarly became more sympathetic through the care he showed for his fellow contestants, especially in his efforts to protect and help Oh as best he could.
However, the ending of the show makes it clear that Oh was more than he initially seemed, as it's revealed that he didn't die in the games as it initially appeared when Gi-hun manages to find him in hospital after winning his Squid Game. In an even more shocking twist, the Squid Game ending sees Il-nam explains that he was part of the formation of the games themselves, having watched them as a VIP for years before joining in Seong's game to have "fun" before his brain tumor killed him. With it becoming clear that Il-nam had faked the kindly old man persona as part of his game plan - and with Gi-hun quickly falling into despair, begging Oh to explain why he let the games go on - the old man offers to make one last bet with his former ally. Pointing out of the hospital room's window to a homeless man lying unconscious in the snow, Oh bets Seong that nobody will assist the man before midnight, even though further exposure to the elements will surely kill him. But what does this say about Il-nam, and how he wishes to spend his final hours?
The immediate answer is that Il-nam simply wishes to prove to Gi-hun that his pessimistic outlook on humanity (and the Squid Game itself) is right. When making the bet, Oh casually refers to the dying man as a "little piece of trash", unveiling a previously hidden disdain for those he deems lesser than him. Knowing that Seong made it through the games with his belief in humanity still somewhat intact, Oh potentially wishes to prove him wrong - only to be inadvertently proved wrong himself when the homeless man is rescued by a person who'd seemingly run off, who had instead gone to find the police to help the man. Ironically, Il-nam never learns that he loses this bet, as when Gi-hun turns to him after seeing the rescue, the old man is dead, saving Seong's faith in his fellow man, but never allowing Oh to change his mind.
However, it is also worth considering that Il-nam both took an especial interest in Gi-hun, and seemingly held a respect for both the Squid Game and its participants, or he presumably would have never wanted to join. He explicitly states that one of the exciting prospects for him was the camaraderie of the games, even telling Seong in the games they are "gganbu" and thus "share everything" when he sacrifices himself to allow Seong to continue on. With all of this in mind, it seems that it's potentially more likely that Il-nam wanted to be proved wrong in his final moments, and made the bet with Gi-hun after watching him continually risk his life to help other Squid Game players. This would make Oh's death far more tragic in this regard - as he would have just missed the final good deed that could have repaired the effects of watching years of the Hunger Games-like events.
Either way, it's clear Il-nam and this final bet leaves a major impact on Gi-hun, as it is part of what encourages him to try to re-enter the games in the final scenes that set up Squid Game season 2. Though he is once again placing himself in a scenario that could very well kill him, this is arguably a far happier fate for Seong than Oh faces - as the fact he's willing to go back to try and make sure he ends the games and helps those about to be in the same scenario he was in proves he still believes in his fellow man.