In Hans Christian Andersen 's The Little Mermaid , it is said that they forget that humans can not breathe underwater , while others say they drown men out of spite . In Hans Christian Andersen 's The Little Mermaid , it is said that mermaids forget that humans can not breathe underwater , while other stories say they drown men out of spite , while still other fables portray mermaids as benevolent toward men .