가는 날이 장날이다.

The Korean idiom '가는 날이 장날이다' (Ganeun nari jangnarida) literally translates to 'The day you go is market day.' This phrase is used to describe a situation where one unexpectedly encounters a special or unusual event, often one that causes inconvenience or changes plans, on a day they had chosen for something else. The idiom's roots lie in the historical significance of 'jangnal' (장날), or 'market day,' in traditional Korean society. Before modern commerce, market days were a crucial part of community life in rural areas. These were specific, designated days when vendors would gather to sell goods, and people from surrounding villages would travel to buy necessities, socialize, and gather information. 'Jangnal' was not an everyday occurrence; it typically happened on a cyclical basis, perhaps every five days (오일장, oiljang). Because market days were special events with bustling crowds, increased activity, and sometimes even festive atmospheres, they could disrupt regular routines or make certain tasks more difficult. For instance, if someone planned to visit a quiet village for a specific purpose, arriving on market day would mean navigating crowds, higher prices, and general commotion, which might not be ideal for their original intention. The phrase encapsulates the serendipitous, often slightly inconvenient, timing of encountering something out of the ordinary. It speaks to the element of surprise and the way external events can unexpectedly influence personal plans. While 'market day' itself was generally a positive and necessary event, the idiom uses it to represent any unforeseen circumstance that deviates from one's expectations for a particular day. Over time, the meaning broadened beyond literal market days to encompass any situation where an unexpected event, good or bad (though often with a slightly negative or ironic connotation), coincides with one's arrival or plans. It highlights the irony of fate and the unpredictability of daily life, emphasizing that 'of all days,' it had to be *that* day. The phrase has been in common use for a very long time, reflecting a long-held understanding of how plans can be altered by unforeseen circumstances.