This pattern conveys a strong emotional inability to do something, often because it would cause suffering, pain, or be morally wrong. It is formal and literary, found mainly in written Japanese, such as novels, essays, or news reports. In speech, it sounds stiff and dramatic.

The verb that precedes に忍びない is usually transitive, describing an action one hesitates to perform on someone or something. For example, one might say 見るに忍びない (cannot bear to look) or 捨てるに忍びない (cannot bring oneself to throw away). The subject is often the speaker, and the emotion is sincere.

Note that 忍びない (from 忍ぶ, to endure) implies a sense of pity or compassion. It is not used for trivial hesitations; it is for situations that genuinely tug at the heart.