迫不得已 is formed by combining four characters: 迫 (to force), 不 (not), 得 (to obtain or be able to), and 已 (to stop). The literal sequence means "forced and unable to stop", where 迫 sets the condition of compulsion, 不 negates 得, and 已 completes the idea of cessation, resulting in the meaning of having no alternative but to act under pressure.