I'm at the library and it costs 20p to use the loos here.
Fine, but I don't have a penny on me. I usually pay for things with my card.
There's no free loo within a 20-minute walk of here. I could probably find a cash machine walking with my legs squeezed together but I can't pay for the loos with a tenner! It would hardly be worth coming back here anyway.
The longer I wait, the worse the problem is going to get, but I can't think of a solution!