Regression to the Mean or High Performing

I had an interesting conversation with one of my Product Owners this week. She thought that over time, planning poker values feel prey to Regression toward the Mean because human nature was such that people didn’t want to stand out and therefore tried to give estimates in line with what they thought others would.

I countered by saying if people were afraid to state what they truely thought the value should be, there is probably a psychological safety issue going on. The purpose of using poker cards during the activity is to avoid anchoring; having everyone influenced by one person stating aloud their estimate. 
After the conversation, another idea crept into my head. I tell teams that small stories are better. I am even a proponent of #noestimates in the right situation. So from this perspective, as a team moves towards high performance, they will get good at vertical slicing and that will lead to smaller stories, and therefore smaller estimate values.

So in response to the original statement, I don't think on a well-functioning team, the estimates are prone to regression toward the mean. However, I can see it happening on a team that is dealing with psychological safety issues. The real test is to watch the velocity over time. If regression toward the mean were happening, the velocity would be dropping over time. If the team is healthy, they will have a steady, or even increasing velocity.