Wiktionary
vb. (context idiomatic English) To act in the least risky manner in a situation in which one is uncertain about the consequences.
Usage examples of "err on the side of caution".
Kindan answered, not knowing what rank the man held and guessing that it was best to err on the side of caution.
Like most Belters, he had always felt the ARM tended to err on the side of caution in their role as technological police.
I don't know what's happening, and until I do I just want to err on the side of caution.
I wasn't sure, and thought it better to err on the side of caution.
Whether any will be bold enough to enter Chataya's in the guise of patrons I cannot say, but I find it best to err on the side of caution.
Dengar had never had much of a reputation, but if he and this woman were hanging around with Boba Fett, it would be better to err on the side of caution.
Both the boy and Chade were eager for us to press on, but I was determined to err on the side of caution after our near disaster.
Neither he nor Gailet had known what to make of Fiben, at first, and had decided to err on the side of Caution.