Intense study of potent arcana, truly rigorous intellectual challenges, and psychically demanding magics can increase one’s strife. Strife represents corruption, despair, fear, loss of resolve, and other mental factors which gradually undo a creature’s very soul. A creature which reaches the 7th level of the strife track suffers a special, permanent effect, which is either randomly selected or decided by the DM. This might involve the creature shutting down completely, or being impacted in such a way that it is forever changed.

Anything that could cause Strife can cause a level of Exhaustion instead.

1. Disadvantage on Intelligence, Wisdom, and Charisma checks
2. Disadvantage on concentration checks
3. Can only take a bonus action or action each turn (not both)
4. Disadvantage on attack rolls and saving throws using Intelligence, Wisdom, and Charisma
5. Suffer the effects of a randomly determined short-term mental stress effect.
6. Cannot cast spells (but can cast cantrips)
7. Suffer the effects of a randomly determined long-term mental stress effect.

Source: Level Up Adventurers Guide