“If the protagonist and his objective constitute the first two important elements in the construction of a story, the various obstacles collectively constitute the third. Without impediments to the attainment of the protagonist’s desire there would be no conflict and no story.” – The Tools of Screenwriting
Before the sea witch gives the little mermaid the potion, she tells her that with every step it will feel like treading upon glass. The mermaid accepts this. Then the witch says that once the mermaid takes human form, she can never return to the sea again. Also, should the prince marry someone else, the morning after he marries another, the mermaid’s heart will break and she will become foam on the crest of the waves. The mermaid agrees to all of this.

The primary obstacle comes in the form of payment. The sea witch wants the mermaid’s beautiful voice. How is the little mermaid princess suppose to get the prince to fall in love with her without being able to speak to him? Still she gave her voice to the sea witch and took the potion.

She drank the potion on the marble steps of the palace. By sunrise, she had legs and before her stood the prince.
