What is a social dilemma? Is it reasonable to assume people might act more cooperatively if they were told that lack of cooperation would be penalized in a social dilemma situation?

In one study, people were (or were not) primed with information about a penalty for non-cooperation ("in a previous study"). What was the effect, in general terms, of this manipulation?
What will be an ideal response?

Answer:
A social dilemma is a situation in which people can increase their personal gain by acting selfishly (uncooperatively), but if all group members act selfishly, then rewards for all are reduced. I.e., cooperation is the way to go, but being selfish is tempting.
When people were told about a "prior study, where people were punished for lack of cooperation," you might think that those told about this would be more likely to cooperate, but in fact, this did not happen. In the study, those who were told about this "prior study" (and the penalty for non-cooperation) were more likely to react by not trusting other members of the group (because distrust had been primed). Thus, those who were told about the prior study penalty were less likely to cooperate.