How do I distinguish CA from KA?

The balance of payments is very simple a concept: the sum of current account and capital account. It is zero. How can we distinguish one from the other? A unilateral transfer of financial assets falls into current account while a bilateral transfer of financial assets falls into capital account. Consider these:
A Canadian buys a car from Japan. This is obviously debit in current account because money, a type of financial asset, moves in one direction from Canada to Japan. It is half the story. Since this Canadian must sell his or her assets for Japanese yen to pay for the car. Since he (she) sells his (her) assets, it should recorded credit in capital account. In this transaction, assets move in both directons unlike buying a Japanese car. The Canadian consumer's existing asset goes out and new assets, i.e., the equivalent amount of Japanese yens come in. The sum of CA and KA should be zero unless there is a statistical discrepancy.