Why can group experiences be challenging for group members?

Why can group experiences be challenging for group members?
 
  a. The role of co-facilitator can be demanding and stressful
  b. With so many people in one group it can be difficult for a member to feel they
  have spoken enough on a particular topic
  c. Often times group members will not get along with one another and be less
  likely to want to engage in the work
  d. Most members will want to dominate the conversation and run the group
  because they like the spotlight and this may serve as a challenge to other
  group members who want to participate