For a few deadly minutes, nobody took care.

There are many possible causes of the Titanic sinking. See: 

http://www.nbcnews.com/science/10-causes-titanic-tragedy-620220 

however one thing is for sure: many circumstances were necessary.

In the movie, James Cameron suggests that the look-out could also have been
distracted by Jack and Rose having fun on the deck. A few minutes was enough
to kill 1514 people.

The pose of Jack and Rose happens sooner in the movie, as they were standing
on the prow of the ship and looking straight forward, the direction the look-out should
be keeping concentrating on, but Rose was still keeping her eyes closed...