By assigning a focus, the player:
gets an immediate modifier to the corresponding attribute.
unlocks related events, diplomatic actions or decisions (ex: theology focus is required to go on Pilgrimage and become a Pilgrim )
eventually receives a lifestyle trait, as a result of prolonged focus (ex: Duelist can be the result of war focus)
There are ten different foci:
Rulership
Business
Hunting
War
Family
Carousing
Seduction
Intrigue
Scholarship
Theology
When expansion is active, improve attribute ambitions (like Obj improve diplomacy.png improve diplomacy) are removed. Instead, the associated events are triggered based on active focus and having less than 8 of the relevant attribute