Not all creatures are proficient with grappling or unarmed attacks. The average person has minimal skill in boxing or wrestling and is not even as skilled as an amateur in those sports. Indeed, some people live their whole lives and never experience an actual fistfight or wrestling match at all. Basic proficiency in these fighting techniques is not universal. With this optional rule, grappling and unarmed striking are forms of fighting that creatures may be proficient in, just like weapons.
You only add your proficiency bonus to your unarmed strikes and grapple checks if you are proficient in striking or grappling.
Unarmed attack = 1d20 + your Strength or Dexterity + your proficiency bonus (if you are proficient in unarmed strikes)
Grapple check = 1d20 + your Strength or Dexterity + your proficiency bonus (if you are proficient in grappling)
Barbarians, fighters, monks, and paladins are automatically proficient in unarmed strikes and grappling.
Rogues, bards, and rangers are automatically proficient in either striking or grappling (player’s choice).
Wizards, sorceresses, scholars, witches, and priestesses are not proficient in unarmed strikes or grappling unless they choose it as a skill or have it in their background.