The "Tristan Chord" from Wagner's opera "Tristan und Isolde" revolutionized music. With its ambiguous tonality, it epitomized the shift towards musical modernism, opening doors to atonality and the dissolution of traditional harmony. Challenging norms, it's a nexus in music history where emotions were expressed through unprecedented harmonic complexity, influencing generations of composers to explore emotional depth in their works. How has a musical piece challenged your expectations or changed your perception of what music can be? Share your experience!