The idea here is to avoid a head on battle with a strong enemy, and instead strike at his weakness elsewhere.

The last was to herself in a savage whisper, furious at her weakness.

The thought made me angry at my own human weakness.

He turned away from her wide, questioning eyes, angry with himself at his weakness.

Even talking seemed to exhaust him and he became frustrated at his weakness.

It was a cry of pure frustration at his own weakness.

You are in this defense; we will run this play at your weakness.

Furious at his weakness, he struggled to sit up and couldn't.

He pushed himself off the bed, wondering at his weakness.

He sat down immediately, a little sheepish at his weakness.