Kiddush 10b: "baki atah b'kol chadrei Torah v'lidrsoh b'kal v'chomer ei atah yodeia?!" - "you are an expert in all areas of Torah and do not know how to darshen a kal v'chomer?!"
Kal v"chomer does not require a mesorah to be used; it is a purely logical inference that one can use to derive a new halacha. R' Chaim (quoted in the Koveitz Shiurim) therefore asks: what does being a baki have to do with being able to darshen a kal v'chomer? Even someone who is not a baki can derive a kal v'chomer with logic?
R' Chaim answers: to darshen a kal v'chomer is simple logic, but to know if the kal v'chomer is correct requires b'keiyus in kol hatorah. How do you know the kal v'chomer you are making does not have some pircha based on a din in taharos, or kodshim, or some obscure gemara?