Here is why I think its such a powerful question:

1. Its safe: We don't know much as kids, so whatever we wanted to be was guided by the small world we understood.

2. It's fun: This brings us back to a simpler time, and when we use LEGO's, this adds to the playful nature of the question, and a playful time in our lives.

3. It's somewhat revealing: Not too deep, but it can show passions that may still be alive today

4. It allows us to see others with more depth and dimension.