It's a question I get all the time. Should the Product Owner take part in your retrospectives?
In short, the ideal answer to this question is "yes". The scrum guide clearly states that there are three members of your scrum team:
- The Scrum Master
- The Product Owner
If the retrospective is a whole-team activity, it stands to reason that the Product Owner should participate.
The pushback, of course, is that if there is tension and/or a lack of trust between the Product Owner and the rest of the team, having the Product Owner participate in the retrospective can prevent the team from discussing the problems it is facing openly.
This, too, is true.
Remember though: not inviting the Product Owner to your retrospectives is agile's version of a Code Smell. In other words, if you feel uncomfortable inviting the Product Owner to your retrospectives, there's likely a deeper issue at play -- and not including her will likely discourage the team from tackling the real issues it is facing.
So, should the Product Owner attend the retrospective? Yes, if at all possible. The PO is part of the team. But, from time to time, it can be helpful to have a closed retro for the rest of the team only.
Just don't get used to it.