Why is Esperanza thumb bleeding?

Esperanza's thumb is bleeding in "The House on Mango Street" after she tries to help her friend, who is being bullied, by defending her and getting involved in a fight. In the process, she accidentally injures herself. The bleeding thumb symbolizes her struggle and the pain that often accompanies standing up for oneself and others. This moment highlights the complexities of friendship and the challenges of growing up in a difficult environment.