Here's why:
* Sonnet: A sonnet is a 14-line poem written in iambic pentameter. It's traditionally divided into an octave (eight lines) and a sestet (six lines). The volta, or turn, occurs between these two sections, usually at the beginning of the ninth line.
The volta marks a shift in the poem's tone, focus, or argument. It can be a change in perspective, a new idea, or a resolution to the conflict established in the octave.
While other forms of lyric poetry may feature shifts in tone or focus, the volta is a defining characteristic of the sonnet.