What realization did he come to regarding his wallet?

The realization that he had forgotten his wallet at the restaurant is significant because it emphasizes a moment of awareness about an oversight that has potential consequences. This choice reflects a specific scenario where the person connects their current situation — likely being without their wallet in a situation where it is needed — with their last known location of the wallet. It suggests a logical deduction process where he retraces his steps and identifies the source of the problem, which is an important cognitive skill in problem-solving.

The other options do not capture this specific moment of recognition. For instance, forgetting the wallet at home or losing it in a cab follows a different narrative path: they indicate a lack of awareness rather than a realization about his actions. Finding the wallet in the car implies he resolved the problem without needing to reflect on where he last had the item, which does not highlight the same cognitive process as the moment of realization at the restaurant. Therefore, the choice that states he remembered he had left his wallet at the restaurant is particularly strong because it encapsulates the idea of coming to an important understanding regarding a misplaced item.