I've been told this game produces some of the most wild experiences but I never believed it. I stopped my first playthrough at X18 (?) a while ago but then started again and wow, playing properly changes everything. 
I had just got back to Cordon after getting the X18 documents this time
>Finish a shootout at farm across from starting outpost
>Walking back to collect RU from various tasks
>See 3 fellow stalkers around fire in tunnel under road (you know the one)
>Share tales, trade, sit down in front of the fire
>Proceed to down 7 bottles of vodka whilst listening to stalkerfriend play guitar, getting super immersed despite spinning screen
>A sudden BEEP on the radar and one of my new friends drops to the ground
>Guitarists swaps his acoustic for something automatic and begins firing upon bush outside the tunnel
>Other stalker begins shooting dogs attacking other side of the tunnel
>I pull out my rifle but the screen is spinning too wildly to use it, I switch to my side arm
>After many missed shots, my Big Ben finally lands a hit into the bush
>I rush up to see a member of the military, merely a private, dying slowly on the ground
>Up beside me walks the stalker who originally had the guitar, who proceeds to execute the soldier
>We go back to the fire, I trade for more vodka, and we rest

Such is life in the zone