You managed to survive an emission without taking cover thanks to the anabiotic pills. The effects of this on your psyche are unclear, as you notice a strange silence inside your mind. It seems that you no longer hear a constant stream of thoughts.
The player can now survive emissions in the open. However, when this happens, the player will pass out and wake up with very little health remaining, which could be deadly if the player is near-immediately attacked by mutants or hostile stalkers.
As stated in the achievement's description, the quiet whispers that are part of the game background ambient (easily heard when the background music is off) will disappear once this achievement is obtained.