We expanded the definition of bookkeeping to companies. First, it is important that right hand side and left must have same amount.

For instance, A company sells a second-handed car with 100K JPY. One company president would like to buy it as a company car with 500K JPY.Of course a company evaluate the car with 100K JPY so that he is so happy to sell it.

The company bought it books this car with 500K JPY.

Vehicle 500K JPY / Cash 500 JPY

On the other hand, the company sold it gives away 100K JPY car and receives 500K JPY.

Cash 500K JPY/ used car 100K JPY

Now left hand side is smaller by 400K JPY, which is a profit.

So when he books 400K JPY profit on right hand side, journal will balance.

Cash 500K JPY/ used car 100K JPY

/Profit 100K JPY

So if we try to keep balance of journals, we automatically calculate profit.

This is the great point of accounting to calculate profit / loss if we keep balance of journals.