Where did the expressionin deep come from?

The expression "in deep" likely derives from nautical terminology, where it refers to being far from shore or in deep waters, suggesting a state of being engulfed or surrounded by challenges. Over time, it has evolved to describe situations in life where one is heavily involved or facing significant difficulties, often implying a lack of easy escape. This metaphorical usage captures the essence of being deeply entrenched in a circumstance, whether emotional, financial, or situational.