Adventuring through the Zone is a dangerous task. Natural dangers are everywhere and competing factions are none too happy about your presence. While a quick trigger finger is a necessity, it's not the only means of survival. In some cases it can actually be a hindrance, as conservation of ammo is a skill that you'll have to master early on.
Like many other FPS titles, STALKER features an impressive array of weapons from simple pistols, to shotguns to full on RPG launchers. On a first run through most players are apt to grab everything in sight only to discover that carrying a veritable arsenal literally weighs you down. That's right, STALKER has a weight limit. Carry too much and your stamina drops like a rock, leaving you vulnerable.
Initially the limit is a bit off-putting, but it forces players to prioritize. Because you can't carry everything, you need to make touch choices about what to load up. Sure, the RPG dropped by an opponent is tempting, but is it really worth swapping out a fully loaded machine gun for a handful of shots with the RPG? That is a question asked repeatedly throughout the adventure. Health packs and armor also count against your weight limit, which means carrying less ammo.