Groupthink occurs when:

Groupthink is a psychological phenomenon where the desire for harmony and conformity within a group leads to irrational or dysfunctional decision-making. The essence of groupthink is centered around the tendency of members to suppress dissenting viewpoints, leading to a deterioration of mental efficiency, reality testing, and moral judgment. When members avoid disagreement to maintain consensus, it can prevent critical evaluation of alternatives, limit creativity, and result in poor decisions.

In this case, the first option emphasizes that members prioritize agreement and harmony over voicing opposing perspectives, which captures the core issue of groupthink. This dynamic can be detrimental because it can result in a lack of thorough discussion about possible solutions or risks, leading to oversights and flawed resolutions.

The other options present scenarios that do not align with the definition of groupthink. While a strong and decisive leader may influence group decisions, it does not inherently cause groupthink unless it stifles open dialogue. Encouraging individual contributions goes against the very nature of groupthink, which is characterized by a lack of diverse input. Lastly, decisions made by majority rule may lead to democratic outcomes rather than the consensus-seeking nature that defines groupthink.