The extensive media coverage of the few major airline accidents that have occurred raises people's perception of the risk. The availability heuristic applies, because deaths by shark are big news and have even been the subject of movies. The representative heuristic would come into play. It is consistent with most people's views of the world to think that wanting desperately to get into medical school would lead someone to fight hard to get good grades. Being given a possible explanation that is representative of how they see the world might thus lead the jurors to give the explanation high probability.
Availability is responsible.
It is much easier to bring to mind words that start with k, by making the sound and seeing what follows, than it is to think of words with k as the third letter. This is caused by being overly optimistic. Most people in their 40s do not think they are about to die. Conservatism might lead a smoker to ignore accumulating evidence that the smoke from their cigarettes harms those around them. Optimism might lead one to drive after drinking, thinking they won't have an accident or get caught.