Around Day 30, the difficulty spikes. NPC factions like "The Cleaners" appear. They do not try to kill you; they try to you for experiments.
Progression is heavily tied to building relationships with NPCs. Completing specific tasks and providing requested items increases their "Affection" or "Love" rating, unlocking new story segments and interactions. A Zombie Life Walkthrough
You can find a book on the floor in the left area of the library; giving this to a character can further increase their care level. Gameplay Tips Resource Management: Around Day 30, the difficulty spikes