The statement describes a specific but common pattern in stock market behavior: an index 'gapping up' at the open (opening higher than the previous day's close) and then selling off during the day. The primary source, 'Historical Data (Nikkei 225)' from the official Nikkei Indexes website, is the definitive resource for verifying this claim. It provides the daily Open, High, Low, and Close values needed to confirm if such a day has ever occurred. To verify the statement, one would need to find a day where the 'Open' price was greater than the previous day's 'Close' price, and the 'Close' price for that same day was lower than its 'Open' price. Given the natural volatility of financial markets, this is a plausible and frequent event. The high authority and direct relevance of the primary data source confirm that the means to prove this statement exist. The other highly relevant source confirms the identity of the index and links to this data. The sources concerning index components or different financial instruments are correctly identified as irrelevant. As the described event is a standard market dynamic and the authoritative data to prove it is available, the statement is highly likely to be true.