Short answers, pulled from the story.
The random encounter feature is a game mechanic that summons deadly foes instantly during exploration to simulate unpredictable dangers. This system emerged from the tabletop origins of Dungeons and Dragons in the 1970s to create a resource management layer that forces players to balance risk against survival costs.
Random encounters became the bulk of battles in genre-defining titles such as Dragon Warrior, Final Fantasy, and The Bard's Tale by the mid-1980s. Early role-playing video games like 1981s Wizardry utilized both placed and random encounters before this shift occurred.
Random encounters happen when the player traverses the game world using a world map or overworld, with the exact moment determined by programmed probabilities and pseudo-random number generators. The simplest algorithm sets a random integer between 0 and 99 for each step, triggering a fight if the number falls below a specific threshold based on terrain type.
Players abandoned random encounter systems because they found the mechanic annoying, repetitive, and discouraging to exploration. The Final Fantasy and Tales series abandoned these systems with successive games, while franchises such as the Chrono series and Kingdom Hearts never used them at all.
Developers replaced random encounters with visible enemies that players can see and choose to engage, as seen in Final Fantasy XII, Radiata Stories, and the Fallout series. A similar approach involves spawning where visible monsters always reappear at the same location, as seen in Chrono Trigger and most of Dragon Quest IX.