Under different circumstances other than World War I it is most likely that Billy Bishop would have been a hapless man with no direction, a string of failed career attempts and uneventful incidents with nothing to show for his efforts. What Billy Bishop Goes To War reveals is that Billy is not a man of great substance but he has a dogged determination. His ability to act without thinking actually works in his favor as he does not stop to consider the consequences of his actions only the potential for great adventure.
The recognition that he has to do something to get out of the "mud" which pervades his existence and his ability to dream, allow Billy, although he knows he has no skills, to grasp onto the ideas that are presented to him. Being an observer gets him close and it is his belief that anything is possible that encourages him. He knows that his "tremendous eyes" are a great asset - if perhaps his only asset - so is prepared to show his mettle by exploiting his one redeeming feature!
Billy has no grand ideas about himself and, even with medals, is still a humble individual. Bill's self-awareness also develops his caracter as he is well-aware of his failings and never actually tries to be anything he is not.