Because the purchase is broken up into installments and paid back monthly. That is why, despite my home being the most expensive thing I have ever purchased, I am not living cheque to cheque. If her problem were the size of the purchase alone, then I too would be living cheque to cheque and so would all other homeowners with mortgages.

Edit: I should point out that my cost of living has actually dropped since I bought my home, because I did the maths to be sure it would. Most expensive purchase of my life saved me money. Go figure, right?