Final answer:
The group asked to recall 6 instances of assertive behavior rated themselves as more assertive due to the availability heuristic, as these examples were easier to recall and thus seemed more common in their memory.
Step-by-step explanation:
The phenomenon where the group asked to come up with 6 instances of being assertive rated themselves as more assertive than the group asked to come up with 12 instances is explained by the availability heuristic. This cognitive bias involves people judging the likelihood of events based on how easily they can recall examples of such events. The group that was asked to come up with 6 instances found it easier to recall such instances and thus, due to the availability heuristic, rated themselves as more assertive because these few instances were more readily available in their memory. Conversely, the group asked to come up with 12 instances likely struggled to recall as many examples, which could lead to lower self-assessment of assertiveness, as they might perceive the task as difficult and assertive instances as less common in their experience.