My buddy, Mark and I have been hanging out on supper dates for the past 18 years. Sometimes he pays first and I forget to pay him back. The reverse happens at other times. We don't trust each other to maintain an Excel file to capture the records. I mean, look, what if Mark doctors the Excel file when I am not looking. This is obviously a great candidate for blockchain - now our records becomes immutable and the history of our misspending are forever etched in the blockchain.