> Avoid debt for things that lose value (e.g. cars).
This is actually not terribly good advice. Debt does not become especially bad depending on whether what you used it for is gaining or losing value.
This rule is really a proxy for, "Don't buy an expensive car, boat, or plane, relative to what you are making." Now that is a good rule. There's no reason to hide it behind a false rule. Financing a purchase that you could pay cash for can sometimes be wise, even if the purchased item is losing value.