Event sourcing can be very appealing for the auditability and replay capabilities it provides. However, when used without care, it can paralyze application development, especially after the original team members move on to other things and are replaced by new team members that were not there when history was written. How can we make efficient use of this pattern to leverage its benefits without being slowed down by the drawbacks? In this talk we will present our experience using it to develop trading engines at the Intercontinental Exchange, and the tradeoffs we made to keep it from slowing us down.