Being on the defensive is a seemingly self-protective attitude when a danger is foreseen or someone who can do us harm. Based on this, we can see that the narrator of the text is on the defensive because he tries to protect himself from his past mistakes by persuading people to believe that he is able to work hard and succeed, as he can prove through his prior grades.
A combining form meaning "father," occurring originally in loanwords from Greek and Latin (patriarch; patrician), and used in the formation of new compounds.
