Iron Will

Patch 2.3.0

 * : removed the while standing still condition from Tiers I & II.
 * : lowered the sound reduction percentage to 75 % on Tier II.

Breathing Volumes
The percentages on both  and its Killer-pendant are misleading in their interaction with one another, as contrary to the popular perception of percentages, they do not represent actual percentages in the Game code, but rather numeric values that are combined additively.

A good analogy is a volume slider ranging from 0 to 100, which can also go above 100 if necessary.
 * Positive values move the volume slider upwards, increasing the volume.
 * Negative values move the volume slider downwards, lowering the volume.

Trivia

 * ' only' affects Grunts of Pain. It does not decrease the sound of the regular breathing all Survivors make across all Health States.
 *  does not work while in the.
 *  is countered by.
 * However,  combined with or  at Tier 3, counters.
 * In the old Game Manual ''' features a different flavour text: '

Eiserner Wille Voluntad de Hierro Volontà di Ferro Żelazna Wola Vontade de Ferro 鋼鐵意志