Why should a boutonniere be worn on the left side of a suit?

A boutonniere is traditionally worn on the left side of a suit jacket because it is closest to the heart, symbolizing love and affection, particularly in formal occasions like weddings. Additionally, placing the boutonniere on the left allows for better visibility and display, as it is typically oriented towards the viewer when the wearer stands or moves. This custom has been maintained through fashion history, reinforcing its significance in formal attire.