Tversky & Koehler (1994) support theory based on availability heuristic - More explicit event descriptions have greater subjective probability for 2 reasons:

The first reason is that explicit event descriptions contain more information which may be easier to remember and recall. Increased recall leads to an impression that such events are more likely to occur than events with less information. The second reason is that explicit event descriptions allow for easier comparison of different events which allows people to identify the most plausible outcome. As a result, explicit events appear more likely than events with less information.