Performers of contemporary music: yeah haha i kinda made up the rhythm there, the notation is 100% exact, because the composer wrote it on a computer and listened to it a thousand times, but i ignored improvised it lol

Actually, it turns out more and more that classical music can be interpreted in many ways, and composers at the time were constantly improvising from a written piece with new ideas on the fly. Contemporary musicians created some kind of a cult to classical music and tried to enforce rigorous exact playing when in reality that was not the composer's intentions at all

Performing medieval music: "sure would be nice if this piece had consistent and readable notation"

Meanwhile Sergiu Celibidache: "Haha, teeeeeemmmmmmmmmmpooooooooooooo gooooooooooooooooooooooooooooooooooo bbbbbbbbbbbrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrr"