Final answer:
Groupthink is the primary obstacle that must be avoided during the norming phase of team formation. It occurs when members of a group modify their opinions to align with what they believe is the group consensus, hindering diverse opinions and leading to faulty decision-making.
Step-by-step explanation:
The primary obstacle that must be avoided during the norming phase of team formation is groupthink. Groupthink occurs when members of a group modify their opinions to align with what they believe is the group consensus. This can hinder opposing trains of thought and lead to faulty decision-making by the group.