Deliberate mistake: When the ship crashes into the dock, all of the scenes leading up to the crash and after it show a clear view across the harbor as we can see lights and land on the other side. It's not until the ship is about to crash that a thick and dense fog appears and disappears within a minute to mask the ship to create a more dramatic effect.
Deliberate mistake: When Sarah, Ian and Nick are climbing up the cliff with the rope, Sarah is able to easily pull the rope up to place her hand underneath it for a better grip. The rope is quite lax for having three full-grown adults hanging from it.
Answer: It's basically about facing one's own mortality. Many humans feel that they 'feel the most alive' when facing (and overcoming) dangerous situations, the more challenging, the better. Roland is a big game hunter, to him, the ultimate challenge would be to hunt the biggest and (presumably) most dangerous predator ever to exist. Facing the danger of the T. Rex would make him feel better and mightier than he had ever felt in his life.
Twotall