Balin, Loremaster

Once you have an enduring story, you have it for the rest of the game, even if you lose control of some or all of your storied permanents. The enduring story designation is on the player and can't be removed by any effect.

A permanent is any object on the battlefield, including tokens and lands. Spells and emblems aren't permanents.

The decision to discard your hand is made during the resolution of the ability, so there is no opportunity for an opponent to respond between choosing to discard your hand and drawing cards.

If you control three legendary, Saga, and/or artifact permanents but don't control a permanent with storied, you don't get an enduring story. For example, if you controlled three artifacts, lost control of two, then cast Thorin Oakenshield, you won't have an enduring story.

You may choose to discard your hand even if your hand contains zero cards.

A single permanent can only count once toward the three legendary, Saga, and/or artifact permanents needed to get an enduring story, even if it has more than one of those qualities. If you control one permanent that is a legendary artifact and a second permanent that is a Saga, you will only have two of the three permanents required to get an enduring story.