Final answer:
The concept of a healing spell being repeated thrice for maximum effect is a fictional idea, often found in mythologies and plays like Shakespeare's "Macbeth" where the number three is depicted as mystical.
Step-by-step explanation:
The healing spell that should be repeated thrice for maximum effect, according to certain mythologies and fictional contexts, would be a ritual or incantation that is often found in stories or plays involving witchcraft or magic.
A well-known reference to the power of three can be found in William Shakespeare's play "Macbeth", where the Three Witches open the play with a chanting that suggests the mystical nature of the number three. However, it's important to note that such practices are fictional and not based in real-world medicine or healing techniques.