"Simplicity is the ultimate sophistication" is a famous quote often attributed to Leonardo da Vinci. It essentially means that the most complex and elegant ideas or designs are often achieved through simplicity and clarity rather than excessive ornamentation or complexity.
In other words, true mastery and sophistication lie in the ability to express complex ideas or create intricate designs in a clear, concise, and uncomplicated manner. It emphasizes the value of minimalism and efficiency over excess.