Why are parents so worried about your grades?

I know grades are important, but isn't there more to life than just letters on paper. I am currently in Honors English and i have a C and I have a B in french. and A's and my 2 other Honors cles. I am in 9th grade and got A's all through middle school. I just told my dad that i have a b in french and he flipped out, and i am afraid to tell him i have a C in English. Do u think i should tell him now, or wait for report cards. I really dont want to do a carer in something in work. I wont to join the foreign legion which is the kind of work i want to do,havent told parents about admiration to join the legion, should i do that too? i want to be able to go to work have have excitement and the risk of dying makes your life existing.