ARC Prize competitor discovers two-session debugging block was built on false assumptions

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A developer competing in ARC Prize 2026 spent multiple work sessions unable to diagnose why their game-playing agent was underperforming on hidden tests. The root cause turned out to be two self-recorded conclusions — that the problem was unreachable on local machines and that practice data was useless — both of which proved false within an hour of direct testing. Rather than revisiting the actual code and game data, the developer had repeatedly relied on their own earlier notes as if they were reliable evidence. Once small probes were run against real artifacts, the failure reproduced cleanly on locally available games, and the practice data revealed the issue immediately. The developer now treats any 'we can't, because' statement as the highest-risk claim in a project, requiring it to be re-verified from primary sources before work proceeds.

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