"Earth is my favorite planet," Ulysses announced.
"What do you like about best about it?" I asked.
I try not to ask why anyone likes what they like. I try instead to invite them to tell me about what they like.
Years ago, in California, I learned that asking "Why do you like x?" can put people on the defensive and shut them down. "Why do you like avocado ice cream?" is really sort of aggressive -- it puts a person in the position of defending the fact that they like what they like. Hence responses along the lines of, "Because I do."
Instead of asking "why," then, we might ask "what." "What do you like best about avocado ice cream?" is more likely to help a person feel more comfortable about sharing. And it's more likely to trigger specifics to come to mind.
In my own thought experiment as I write this, my internal response to "Why do you like avocado ice cream?" was "I just like it. It's good." And I felt a little silly for liking avocado ice cream as I thought it. When I asked myself "What do you like about avocado ice cream?" my answer came as "It's rich and creamy and tasty."
Then I asked myself "What do you like best about avocado ice cream?" Interestingly, this question had the most comfortable feel of all. Somehow it triggered the most specific details immediately. I thought, "Such a pretty shade of deep green. Such a velvety mouthfeel. Such a luscious, silky, aroma. Such a delicate flavor." I could see and feel the scoop digging into the tub. Also I like it that the flavor of avocado goes so nicely with sweet. I never would have thought it!
Back to Earth.
Ulysses answered, without hesitation, "It has green grass and blue water."