What is the author's credo? What is your credo?
Certainly, Fulgham's credo would be to embrace the world as one learns to do when in Kindergarten. The world that one sees in Kindergarten is one filled with optimism, a sense of adventure, and the understanding that there are opportunities in life wherever one "looks." Outside of the 16 rules that the book puts forth, I think that being able Fulgham would define his credo as being able to appropriate the world in accordance to one's kindergarten subjectivity. The ability to reach back into the psyche and pull the way that life appeared at the most elemental of stages becomes a secret to being happy with one's self, one's world and one's place in it.
The credo that Fulgham embraces is startling in its simplicity, but is also a condition in which its approach to being is universally applicable. A credo that can be seen in the same context would be one in which individuals live by their doing their duty and avoiding the fruits of one's labor. In a similar way to Fulgham's approach, the idea of doing one's duty for its own sake cuts through the veneer of experience and supposed maturation and strives to view the world in the way a child views it. Love of what one does for the sake of doing it as opposed to what is attached to it could be seen as a credo that defines one's being in the same capacity as Fulgham's.