Yes! Checks. Those historic relics that are unnecessary because we can do everything electronically now.
Consider these recent experiences I had transferring funds from one of my accounts to another:
Attempt 1: I wrote a check to myself from one of my accounts; went into bank and deposited it into another account.
Result 1: Funds were posted to the deposit account immediately and deducted from the paying account when the check processed a couple days later.
Attempt 2: Set up online transfer of funds from one account to the other online.
Result 2: Funds were deducted from the paying account the day after requested. Funds disappeared into the abyss and still haven't appeared in the deposit account 5 days later. I did notice a note when I checked online status that the funds would be there by Nov. 1 (for a transfer requested on Oct. 25).
So, where did my money go? I can only assume it has been compounded with other funds in some transfer account somewhere where for 5 days it is earning interest of the sort that only ever benefits or is available to financial institutions.