The first thing Stalker does is teach you to be a coward.
There's no deliberate instruction involved- it's a lesson you learn naturally, which makes it ten times as effective. The tutorials are the pack of wild dogs who maul you because you tried to shoot them, the anomalies that reward your curiosity with poison and radiation, the handful of men that kill you five times over despite the quicksave which puts you in a perfect ambush position.
With uncharacteristic speed, your subconscious gets the message: this is not a world that was tailor-made for your pleasure. The gun in your hand was not placed there by God, so that you could accomplish a mission He has laid out for you. The dangers you see are not elements of a meticulously arranged shooting gallery- they are dangers pure and simple, under no kind of obligation to compensate you for the hardships they incur.
Ten minutes into Call of Pripyat, I found my first camp. A young man squatting by the campfire referred me to the boss, who I found on the other side of a nearby cargo container. My gamer instincts relaxed as I entered familiar territory: An NPC I interacted with via a conversation tree, ready to dispense basic exposition at the press of a button.
As I asked him about the availabled missions in the area, our conversation was cut short by the sound of a shotgun blast- the dialogue box literally closed while I was still reading his answer. While I blinked in confusion, the man turned away and took cover up against the wall. Drawing his gun, he started moving back towards the campfire. I saved the game and followed him. The bandits who had just killed the guy at the campfire shot us both dead in seconds.
I loaded the game. He advanced towards the campfire. I backed away and watched as the bandits shot him dead again. When I moved closer, they saw me and muttered warnings; I holstered my gun, and they went on their way.
The two corpses at my feet were a sad thing, but I didn't really feel guilty. After all, I didn't know these guys; we were just talking. I was just relieved those bandits hadn't cared about me.
I didn't want any trouble.