Several hours before the ship bumped into its Celine-Dion-scored doom, another ship, Mesaba, had sailed through the same area. Upon seeing Jack Frost's idea of a honeymoon location, they sent out a message to all ships in the region (including the Titanic) warning of a "great number [of] large icebergs." With that, they considered their job done, and hoped that nobody was foolish enough to ignore their message.
The crew of the Titanic had received all of the messages sent by Mesaba. Unfortunately, several days beforehand, the ship's radios had broken, leading to a massive backlog of messages to be received, transcribed, and hand-delivered to their respective passengers. And unlike so many of those texts from a clingy ex, many of these messages required replies. All in all, the crew was going through about 250 messages per day -- so about the same amount of daily texts from that clingy ex. One of the radio operators eventually collected the Mesaba's message for delivery. However, he didn't realize how important a giant field of icebergs would be, and ignored it until he'd finished his other deliveries.
"Meh. If it's important, then they'll send it again."
At the post-sinking inquiry, it was determined that the failure of the crew to deliver this message to the bridge had directly led to the ship's sinking. After all, binoculars are all well and good, but the best way of avoiding an icy grave is to not go there in the first place. Although being "unsinkable" couldn't have hurt, either.