The HttpKernel dispatches an event and every listener registered years ago fires, in an order nobody chose deliberately, doing work nobody has reviewed since. You know how that goes.

You have listeners too. Behaviors registered early, in circumstances that made sense at the time, still firing on every event today. Some of them made you a good engineer. Some of them are quietly working against you, and like any legacy listener they're hard to see precisely because they have always run.

This is a mostly non-technical talk about the habits developers carry, using a component you already understand as the way in. No prior knowledge required beyond having been a person for a while.