Inefficacy

ˌɪnɪˈfɪkəsɪ

noun

lack of power or capacity to produce the desired effect

The word 'inefficacy' highlights the inability of something to achieve its intended purpose or desired effect. It underscores the concept of inefficiency and ineffectiveness in a concise manner.

Supposing this person, wearied at the inefficacy of the poison, should, as Monte Cristo intimated, have recourse to steel!—What if the count should have no time to run to her rescue!—What if her last moments were approaching, and she should never again see Morrel!

Alexandre Dumas

The Count of Monte Cristo