It seems like you are reasoning to be living one year out of thin air and be able to accumulate in that year 200,000 US$ to be used as the down payment for the

It seems like you are reasoning to be living one year out of thin air and be able to accumulate in that year 200,000 US$ to be used as the down payment for the 1,000,000 house. Since you cannot live with nothing, it will take you more than one year to save those 200,000, and don't forget that for many years later you will have to pay the mortgage on the "other" 800,000 dollars.