  We analyze an extended model of the Iterated Prisoner's Dilemma where agents
decide to play based on the data from their limited memory or recommendations.
The cooperators can decide whether to play with the matched opponent or not.
The agents' decisions are directly linked to their level of optimism since they
decide to play if they believe the opponent has a high probability of
cooperating. Optimism is precisely tuned by parameters optimism threshold and
tolerance. Our experiment showed that being optimistic is better for
cooperators as it leads to more accurate exploration in the multi-agent system,
which tolerates the vulnerability against defectors.
