The engineering challenges, I will say, were my favorite. Being challenged to apply our knowledge of certain areas of science to a physical, tangible model that we create is a great part of giving a lift to understanding a concept to our full extent. Not only is it fun, but, in the end, it helps us learn from our mistakes and go further.
I don't believe in any projects did I necessarily fail. Most of the creations were successful, to a certain extent, thatks to the basic knowledge of science I have.