Have some friends who had shitty credit in college jump on board the Dave Ramsey wagon. They cancelled their cards, were paying down the balances, and gradually building up savings.
Several months went by and they ran into some major car issues that adding up to several thousand dollars. The guy's company also needed him to travel for work for a couple of months -- since it was a small company, they didn't have a corporate card, so wanted to reimburse him every couple of weeks for his actual expenses.
At that point, they were completely mumped. Not enough in savings yet to pay for the car expenses, and no way to pay for plane tickets/hotels/meals/etc. on the road until reimbursement. They ended up having to get a loan from the in-laws to pay for the car expenses, and beg for help from work to pre-expense some of the stuff.