The question is not if you're carrying $400 in cash, but whether you can afford that expense. A credit card paid off in full is considered cash-equivalent: "When faced with a hypothetical expense of only $400, 59 percent of adults in 2017 say they could easily cover it, using entirely cash, savings, or a credit card paid off at the next statement (referred to, altogether, as “cash or its equivalent”)" (from the same page of that report).