Around the bend

Origin

The image of a road or river that disappears "around the bend" is quite vivid: you can't see what's coming next, or where it leads. This literal sense of the unknown, of a path that veers sharply out of sight, began to be applied metaphorically to a person's mental state in the early 20th century. To "go around the bend" meant to deviate from a straight, rational course, much like a vehicle or boat veering unpredictably. It captured the unsettling feeling of someone whose thoughts or behavior suddenly became erratic and unpredictable, as if they had taken a sharp, unseen turn into the realm of irrationality, leaving their sanity behind.