We've got to check our stuff all the time. As for mooring failures, it happens frequently. We lose boats to pennant chafe every year in my harbor, and it doesn't make the news. Chain and swivel failure is less common because the regulations require the ground tackle to be pulled and inspected every 3 years.

A friend had $60k in damage to his boat (in another harbor in CT) after it went adrift in fairly calm conditions and ended up on rocks. He wasn't insured, but fortunately was able to recover most of the $ from the mooring operator, but not without legal expense. It was a rental mooring -- this is a picture of the failure mode. The owner of the mooring claimed it was inspected. Yeah sure. I offer this as evidence, your honor.