Using a large, typically crowded commercial building with wall to wall aisles of shelving, displays and merchandise like a Super Walmart as an example where a crazed shooter decides to start killing. The shooter could be anywhere inside the building when they start firing, --- standing right next to you, completely on the other side of the building, or anywhere in between.

Panicked crowds crying, screaming and running in all directions at the same time, all trying to get as far away as possible but uncertain where the sound of gunshots are coming from due to the chaos and loudness, echos and deflection by shelving, merchandise, etc.

Maybe there also could be other terrified ordinary gun carrying citizens with the same intentions of trying to put a stop to the shooter if they get a chance that one may encounter between you and were ever the crazed shooter is. Neither you nor they know for certain who or what the shooter looks like, how they are dressed, is at at any given moment, or, if there could be more than one crazed shooter.

Now plan from there...