There is no historical evidence to suggest that Gaius Julius Caesar, the Roman statesman and military general, ever made the statement, "As a rule, men worry more about what they can't see than about what they can." The quote does not appear in any of his known writings or contemporary accounts of his life.
It's worth noting that while Caesar was a prolific writer, most of his works have not survived to the present day. The majority of information about his life and accomplishments comes from ancient historians and writers like Plutarch, Suetonius, and Julius Caesar's own Commentarii de Bello Gallico (Commentaries on the Gallic War).
Therefore, it's important to be cautious when attributing quotes to historical figures without verifiable sources. While the sentiment expressed in the quote may have some philosophical or psychological validity, we cannot confirm that Caesar was the one who said it.