Origin

The character 癖 combines a classifier for illness or physical conditions on the left with the character 辟, which sounds like "heki" and provides the pronunciation hint. The idea is that a habit or mannerism is something that sticks to a person like a condition or quirk of the body—an ingrained trait that won't go away. Over time, the meaning extended from physical peculiarities to include behavioral habits and personal quirks more broadly. The sound component guides you to the "heki" pronunciation, while the illness radical on the left anchors the sense of something persistent and characteristic.