Here's why:
* Regular Plurals: Most nouns form their plural by adding "-s" or "-es" (e.g., cat/cats, box/boxes).
* Irregular Plurals: Some nouns have irregular plural forms (e.g., child/children, goose/geese, mouse/mice).
* Other Changes: Sometimes, even adding "-s" or "-es" requires further changes, like changing the vowel (e.g., man/men).
So, while there are some exceptions, the spelling of a noun often changes when making it plural.