"Horton Hatches the Egg," by Dr. Suess

    On doing what you say you’ll do: “I meant what I said, and I said what I meant. An elephant’s faithful—one hundred percent.” Horton Hatches the Egg by Dr. Suess

I enjoyed this book as a child and continue to find it inspirational as an adult because of the fierce determination Horton the elephant had for completing a task.  Horton never gave up even when the challenges he faced seemed impossible for him to complete his committment.     
 He endures harsh environmental elements, is ridiculed by his friends, and is captured by hunters and forced to be in a circus.  Yet, through it all, he is committed to keeping his word and is ultimately rewarded in the end.