The letter will not make or break the loan, but let me be honest and say the more tragic, and promising the incident was isolated is the best way to approach the request.
SOME REAL EXAMPLES
1) kids on drugs who stole our money,,,,,,,they are now in jail doing time so it wont happen again.
2)I worked in a psychiatric ward as a nurse, and was pushed out a plate glass window by a crazy patient.
3)My payments were late because I didn't have the money, if I don't get this money it will be your fault I am late again.
Now as you can see #1 is OK because if your thieving kids are locked up for a bit you may do OK until they are paroled, #2 was so sad half my office was crying because the woman included her lawsuit, and pictures from while she was in the hospital, and #3 I believe found his file at the bottom of every stack of files, a hundred new conditions, and we reran his credit to make sure he paid his bills during the process of his loan. The letter is just a formality, and it is only requested to weed out the idiots like example #3. Most mortgage brokers are aware some borrowers are not smart enough to realize the bank does not have to lend anyone money, so they will write the letter for the borrower to sign