Ορισμός και Σημασία του "[run] deep"

What is the origin of the idiom "to run deep" and when to use it?

The precise origin of the idiom "to run deep" is uncertain. However, it appears to have emerged during the 15th century, with usage examples from the 1400s. The idiom is more generally used to convey the idea that something is deeply ingrained, established, or persistent. It can be used to describe feelings, problems, beliefs, involvements, or interests.