When you get a raise or accumulate some savings, you may find yourself confronted by an instinct of modern civilized men and women. The desire to spend money. It begins simply, by going out to restaurants, then accelerates to purchasing clothing, electronic gadgets, and  the automobile, you may even buy a new car. If you're married or ambitious, a few months later your thoughts eventually turn toward buying your own home.  Or a move-up home, if you are already a homeowner.
Next, you contact a loan officer to get prequalified for a mortgage loan.  You state your desired price and how much you can put down. You provide your income and may even supply pay stubs and W2 forms.  The loan officer methodically crunches the numbers  (by telephone, in person, or even over the internet).
If only you didn't have this car and the payment...