There are several reasons why a man might walk on the outside of the sidewalk when walking with a woman or another person:

• Protection: Traditionally, the man would walk on the outside to protect the woman from potential hazards such as splashing water from passing carriages (historically) or cars, or from being jostled by passersby.
• Courtesy: It is seen as a sign of politeness and chivalry to offer the "safer" position to the other person.
• Social Norms: While less common now, the practice stems from older social norms and gender roles where men were expected to be protectors.
• Situational Awareness: The person on the outside might be more aware of approaching traffic or other potential dangers, acting as a "buffer."

While the specific reasons may vary and the practice is becoming less common, they generally relate to protecting the other person and displaying courtesy.