A couple of weeks ago I ended up in a technical debate on how to take an existing Event Sourced application further to fully reap the benefits it is designed to give you. I’ve written many posts about the pitfalls, the best practices and how to implement this in .NET specifically. But after 10 years of Event Sourcing, I still think it is useful to provide you with a list of the most important guidelines and heuristics that I think are needed to be successful with Event Sourcing. I'll talk about aggregate boundaries, appropriately-sized events, cross-domain communication, optimizing projection speed, aggregating data and more.