The word "悔恨" is formed by combining the characters "悔" and "恨", both containing the heart radical (忄) to signal emotion-related meanings. "悔" uses the phonetic component "每" to approximate pronunciation and conveys regret, while "恨" uses the phonetic "艮" for pronunciation and denotes resentment. Together, they create a compound word meaning deep remorse or bitter regret, where the heart radicals emphasize the emotional aspect, and the phonetics guide reading.