Changing the user interface can have major unexpected consequences.
Back in the 80s, the company internal telephone system was updated. The new system examined external calls and sent them by the cheapest route - BT, Mercury, or up the leased line to head office.
Old system: Pick up phone, get internal dial tone. Dial 9, external dial tone. Dial number.
New system: Pick up phone, get internal dial tone. Dial 9, system waits for the external number with no dial tone then works out the cheapest route.
Nobody, not even the switchboard, was warned in advance about this change.
In a large office building, large numbers of people thought there was a fault. Many of them tried pressing the 9 key again and again to try to get the external dial tone.
The telephone system watched the key presses until it recognised a valid number, then dialled that number.
Note to non-UKans: The UK emergency number, roughly equivalent to the US '911', is '999'.
Biting the hand that feeds IT
