Kun'yomi are characterized by the strict (C)V syllable structure of Japanese words (yamato kotoba).
For instance, the character for east, 東, has tō as its on'yomi, from Middle Chinese tung.
For instance, the word なおす, naosu, when written 治す, means "to heal an illness or sickness".
As a result, native speakers of the language may have trouble knowing which kanji to use and resort to personal preference or by writing the word in hiragana.
承る uketamawaru, 志 kokorozashi, and 詔 mikotonori have five syllables represented by a single kanji, the longest readings in the jōyō character set.