Music and Poetry
A Raga is bound within the limits of the Saptak. A musician improvises new melodies on stage, but all those improvisations are within the Svars that form the structure of the Raga. The slightest of alteration can change the whole Raga, its bhaav, and the emotion it is supposed to invoke. Once the musician's mind and soul merge with the Raga, music just flows. There is catharsis for musicians and their audience in the music that comes out at that point.
Similarly, writing is bound within the limits of alphabets. No matter what a writer creates, the basic structure, the alphabets, remain the same. Once the writer's mind and soul merge with a subject, words just flow. There is catharsis for writers and their readers in the poetry that comes out of them at that point.