[Question] Only optimize to 95 %

I was reading Tom Chivers book “The AI does not hate you” and in a discussion about avoiding bad side effects when asking a magic broomstick to fill a water bucket, it was suggested that somehow instead of asking the broomstick to fill the bucket you could do something like ask it to become 95 percent sure that it was full, and that might make it less likely to flood the house.

Apparently Tom asked Eliezer at the time and he said there was no known problem with that solution.

Are there any posts on this? Is the reason why we don’t know this won’t work just because it’s hard to make this precise?