Professor Steven comes to rescue the thread:
Debt: not a good thing or a bad thing an of itself. Undisciplined debt, unwise debt, unfounded debt is bad. Certain debt spending can be good, even when one has sufficient cash on hand, but I'll spare you the economics lesson (I paid thousands of dollars for mine, you can too!).
The trick is avoiding so called "bad" debt. This includes things like cars, Christmas loans, personal, and often, credit cards.
So called "good debt" is debt that will return you a profit. Debt such as a home mortgage, or a student loan will eventually turn up as being positive. Face it, most people don't have tens or hundreds of thousands of dollars to get educated or purchase a home, so debt is necessary.
Now, in order to get "good debt" (a home mortgage, for example) requires going to someone who does have the money - usually a bank. The bank wants to protect their loan and earn a profit, just like everyone else, so they charge interest and require proof that you are worth lending to. They do this a number of ways, but the two biggest ways are through a credit rating and by appraising the value of your home. A credit score is not an "imaginary number", but a carefully calculated "value" that determines how likely one is to pay back debts. A credit score is simply a number value representing financial trustworthiness.
The way to get a good credit rating is, unfortunately, by getting other debt and paying it back. As has been mentioned, the easiest way is with a credit car. By wisely and prudently spending on a credit card and paying it back in a timely manner, one can build good credit. By not making stupid purchases that one cannot afford, and by paying off their debt, one can get effectively use a credit card wisely. Of course, most people are not wise, and charge on things they cannot afford to pay off quickly, thus incurring higher interest rates and penalty fees. This is the trap of credit cards.
Personally, I have had a credit card for nearly 10 years. My credit rating is just above 800, when I checked in June to apply for my mortgage. I have "no" debt. My credit card balance is $130. I have been using my credit for nearly all purchases since I was in high school, and paying it off, completely, each month with cash I earned at work. This is how to properly use a credit card.
Manual underwriting is a thing of the past, and most (if not all) lenders don't practice that anymore. Those that do usually charge higher interest rates, or are not willing to loan as much. A lender will not, will not lend one large amounts of money simply based on an account balance. Account balances do not indicate how likely one is to pay back a loan.