https://www.gamespot.com/articles/how-sea-of-thieves-progression-system-ensures-you-/1100-6455647/

Although Sea of Thieves can be played solo, cooperative multiplayer is a major component. Oftentimes, friends can have trouble playing co-op games together if they haven't invested the same amount of time in them, but with Sea of Thieves, developer Rare has its sights set on a progression system that works differently.