Pokémon RPG games are littered with mechanics that bring specific stat buffs and nerfs to the cute little Pocket Monsters.
One of these mechanics is Natures, a random “role” that influences how a Pokémon’s stats grow as they evolve and level up. Natures have been a mainstay in the Pokémon series since the Game Boy Advance games.
Natures are always present somewhere in the Pokémon summary page. They come in many forms, including Naive, Lonely, and Adamant (to name a few).
A Pokémon is given a random Nature when it’s caught, hatched, or obtained by a player. There’s no way to control the Nature of a Pokémon, which can lead to some trainers being frustrated as they try to find the best one for their team.
Obviously, some Pokémon are better suited for a particular Nature. You wouldn’t want a physical attack dealing Pokémon, for example, to have a Modest Nature because it decreases the Attack stat while increasing Special Attack, which you’ll never use.
For a better look at what each Nature does, Bulbapedia has a chart set up to let you know which stat is increased and decreased depending on a Pokémon’s Nature.