The Retrospective is about how the work was done, not the work itself. Have everyone focus on processes or behaviors that were beneficial or caused problems delivering the planned work, and on previous retrospective commitments1 and whether they were satisfied.
Remember that other parts of the organization don't see you as individuals, but a team. As a result, there is shared accountability within the team to produce high quality work that satisfies the needs of organization.
The Retrospective is "Blameless", meaning its important to think about success and failure at the team level, not individual. If you are addressing a behavior, think carefully about how to frame it in such a way that it is not obviously calling out team members.
The Retrospective can be hard at first, but don't stop. In a few months your team will begin to openly talks about success and failure with a genuine desire to improve.2
Some things to remind your team when getting started.