Why does Tom make up his mind to run away?

Tom becomes even more crestfallen when Becky snubs him in the schoolyard. Like he does with Aunt Polly, he attempts to win Becky's attention by "showing off."In his plight of loneliness, Tom decides that society has forced him to go into a life of crime. Tom meets with Joe. Joe, whose mother had whipped him for drinking cream (a crime of which he was innocent), is in tears and has decided to lead the life of a hermit; but after Tom's persuasion, Joe agrees that a life of crime would be more desirable. So the two boys, determined to become pirates, plan to run away from home and live on Jackson's Island: an uninhabited, narrow, wooded island in the middle of the Mississippi River.