Running self-check does not write to the database. I envision `events` to be events that change the database. The way I've been thinking about `pid1` is in the events view on profile page - if we want to show that in the history of that particular user, we set `pid1` to that user. Does it make sense? If we can come up with something that should not be shown in a history of any user we can lift the non null requirement.

Making it looser later on always appeared to me easier than tightening things up when they are not ready for it.