why did tissaia kill herself

Tissaia killed herself primarily due to overwhelming guilt and despair following the catastrophic events of the Thanedd Coup, which she felt responsible for. She was devastated by the destruction at Aretuza, betrayal by her lover Vilgefortz, and her failure to prevent the ensuing chaos and deaths. She also physically weakened herself by casting a powerful and taxing spell, Alzur’s Thunder, during the battle. Feeling hopeless, that her time as a powerful sorceress and mentor had ended, and burdened by the perceived irreparable harm to the relationship between sorcerers and normal people, Tissaia took her own life. She left a letter for Yennefer, expressing poignant reflections and entrusting her with the leadership of Aretuza before her death. This complex mix of guilt over the coup's aftermath, heartbreak over betrayal, and the heavy responsibility for the destruction led Tissaia to see suicide as the only option, marking the end of her role as a unifying figure among the sorcerers and paving the way for Yennefer to rise in her place.