This quote offers a fascinating perspective on the nature of detective work and its role as a mental exercise. The speaker presents sleuthing not merely as a hobby but as a wholesome activity that caters to human curiosity and intellect. Engaging in detective work is portrayed as an advantageous alternative to more harmful introspection or overwhelming mental distress, suggesting that pursuits stimulating the mind can serve as productive outlets for our natural inquisitiveness. The emphasis on it being 'harmless' underscores its safety and suitability as a form of entertainment or mental engagement.

From a psychological viewpoint, having an active mental pursuit like sleuthing can provide a sense of purpose, focus, and engagement, which are crucial for mental health. When inner thoughts turn too dark or overwhelming, diverting attention to solving puzzles or unraveling mysteries offers an external challenge that keeps the mind occupied and invigorated. The phrase 'not too strenuous, not too sedentary' highlights a balanced approach—challenging enough to stimulate but not exhausting; active enough to prevent stagnation.

Furthermore, this perspective elevates detective work from mere recreation to an almost therapeutic activity, reinforcing its nobility and utility. It hints at a philosophy where mental activity, curiosity, and problem-solving are essential components of mental health. Engaging with mysteries invigorates the mind while potentially warding off destructive thoughts or habits. This approach encourages embracing curiosity, intellectual pursuits, and storytelling, which can serve as constructive expressions of human nature.

Overall, this quote celebrates the power of engaging with the mind creatively and responsibly. It champions detective work as a noble, enriching pursuit that nurtures curiosity, sharpness, and mental well-being while serving as a safeguard against more harmful inner struggles.