Currently I feel there is nothing to differentiate completing a challenge with an Uncertain Outcome from making a move that does not complete a challenge. (By playing a non-completing card, or not playing a card at all). By leaving the outcome entirely up to the narrator, it feels like there is nothing to incentivise the player to complete a challenge in this way.

While there are tactical benefits to playing cards early and often, there are also benefits to marshalling them. Playing a card to complete a challenge with an uncertain outcome therefore feels like a wasted card, as it does not grant the player narrative control as completing with a strong or weak outcome would.

I think there are a couple of changes that could make an uncertain outcome more satisfying. One of these would be for the player to narrate a "mixed" outcome - some good, some bad. Another would be for the player to set up the outcome, but leave final narration to the Narrator. (I like the idea of the player framing their action, then asking the Narrator a leading question about what happens next. "What do I learn that I wouldn't have done if things went smoothly?")

The big disconnect for me is that completing a challenge with a Strong or Weak outcome is a "win" for the player, even if it's bad for the character. The Uncertain outcome feels like a "lose" for the player, with no compelling reason to choose it. I think the Uncertain outcome needs to be given a bit more depth and player involvement than just "Narrator decides" to make it a meaningful choice.