Final answer:
The term describing the common approach to optimism shared within a group is 'groupthink', which often leads to consensus at the expense of individual perspectives.
Step-by-step explanation:
The term for the idea that groups tend to share a common approach to optimism is groupthink. This phenomenon occurs when group members modify their opinions to align with what they believe is the group consensus. Symptoms of groupthink can include perceiving the group as invulnerable, believing the group is morally correct, and self-censorship by group members. This consensus within the group can sometimes lead to suboptimal or flawed decision-making because it hinders opposing viewpoints and fosters an environment where the unity of outlook is overly emphasized.