It was perhaps the most catastrophic lapse of memory in history, costing more than 1,500 lives.
A sailor called David Blair forgot to leave behind a key as the Titanic set off on its maiden voyage.
Without it, his shipmates were unable to open a locker in the crow's nest containing a pair of binoculars for the designated lookout.
The binoculars were to look out for dangers in the distance including signs of bad weather - and icebergs.
Lookout Fred Fleet, who survived the disaster in which 1,522 people lost their lives, later told an official inquiry that if they had binoculars they would have seen the iceberg sooner.
When asked by a US senator how much sooner it might have been spotted, Mr Fleet replied: "Enough to get out of the way."