The sinking of the Titanic is perhaps one of the greatest tragedies in the history of ocean travel and the question at hand has been asked countless times in the decades since. It is impossible for a definitive answer to be given. Ask two historians, get two different answers. Ask two more and neither will repeat the first two.
It seems that circumstances worked together against the majestic ship.
1. More icebergs were released from the ice packs to the north that year because of a warming trend.
2. The belief that the ship was unsinkable probably caused the captain to take more risks than he otherwise would have.
3. Someone had locked up the binoculars that the watchman would normally have been using.
4. Believing in the strength of the mighty ship's hull, the steersman steered into instead of away from the iceberg.
The list could go on but as you see no one person or circumstance can be isolated so as to say "this is the cause."
The thing that made the tragedy so great was the fact that there were not enough lifeboats on board; even though that was not illegal it was one of the points that would be debated for years. Of the ship's 2200 passengers there was only room for 1200 if every seat in every lifeboat had been filled. But that is another question.