In what way is Pudd'nhead Wilson's remark about the dog the key to the whole book?

Hearing a dog barking and yelping, he comments that he wishes he owned half of the dog. When asked why he desired this, he replies that he would kill his half. This remark struck the townspeople as completely moronic - if Wilson killed half of the dog, surely the other half would expire as well. Thus, if he is going to kill the entire dog, why only wish for half? The town was convinced that Wilson was a fool, and from that day forward he was stuck with the nickname "Pudd'nhead." Though he would eventually come to be well liked, the nickname would remain.

Wilson's ill-timed "half-dog" remark makes him the subject of constant ridicule. He is unable to jumpstart his law practice and is largely rendered a non-entity in Dawson's Landing. Twain thus reveals that while there is no guarantee for its accuracy, a person's reputation can have a considerable impact on the course of their life.