When you make a promise to someone, it is as if you take a debt from them. The
‘debt’ you owe to the person is not paid until the promise is fulfilled.

In the poem ‘The Cremation of Sam McGee‘, the Canadian poet Robert A. Service
writes, ‘ _A promise made is a debt unpaid._ ‘ The poem is the tale of a Yukon
musher keeping a promise he made to cremate his friend rather than let him be
buried in the ice and snow.