Two Pokémon of the same species at the same level do not have the same stats. The difference comes from two hidden values: IVs, which are innate, and EVs, which are earned in battle. Sun and Moon finally make them easy to master.
IVs (individual values) range from 0 to 31 for each stat, set at birth or capture. EVs (effort points) build up in battle: 252 at most per stat, 510 in total. At level 100, 4 EVs give one stat point, and 31 IVs give 31.
The seventh generation brings two decisive tools: the IV Judge built into the PC, and Hyper Training, which lets you max out imperfect IVs.
