Final answer:
An antonym for a line delivered with self-doubt would be a line delivered with confidence, conviction, or assertiveness, which conveys a strong, clear, and certain tone in contrast to hesitance or uncertainty.
Step-by-step explanation:
A line delivered with self-doubt is typically characterized by hesitation, uncertainty, or lack of confidence in the speaker's tone or choice of words. An antonym for this would be a line delivered with a sense of confidence, conviction, or assertiveness. Confidence in speech implies that the speaker believes in what they are saying and conveys a strong, clear, and unwavering tone. Conviction might be accompanied by evidence or strong belief in one's opinions, and assertiveness communicates a firm stance on the subject at hand.
For example, the bold, defiant, and self-righteous tone in the provided text illustrates a stark contrast to self-doubt. When the woman says, "Yes. It keeps me from having panic attacks," she does so defiantly, and the airline employee retreats. This is a clear example of a confident and assertive delivery. In contrast, expressions of self-doubt are often veiled in hesitation, like the characters debating their precarious situation without voicing their pessimism directly.