Jekyll drinks the potion to transform into Hyde.
Here's why:
* The potion's effect is to unleash Hyde: The potion is designed to separate Jekyll's "evil" side, represented by Hyde, from his "good" side. It's not a two-way street, but a one-way release valve.
* Hyde's existence is a consequence of the potion: Hyde is a manifestation of Jekyll's repressed darker impulses. He doesn't exist without the potion.
* Hyde's transformation is spontaneous: Hyde's transformation happens without any conscious action from Hyde himself. It's an automatic effect of the potion wearing off.
Think of it like a dam holding back a river. Jekyll is the dam, and the potion is the valve. Hyde is the river, and he bursts forth when the valve is opened.
It's a critical element of the story, emphasizing the struggle within Jekyll and the nature of the "good" and "evil" sides of humanity.