event-taxonomylisted

# Event taxonomy The most expensive measurement mistake is not a bug. It is one event covering two things worth different amounts. ## The mechanism A campaign optimising for a conversion *count* will find the cheapest instance of that event. If a low-priced trial and a full-priced subscription both fire the same event, the system learns to find trial buyers, because that is the cheapest way to produce the number you asked for. Nothing is broken. You are paying the platform to avoid selling the expensive thing, and the reporting shows the campaign hitting its target while it does so. ## The fix **One event per commercial step, with a written definition.** Use the platform's standard events where one fits the step. They need no setup, they carry the platform's own behavioural priors, and other tools understand them. A custom conversion is a *filter defined on top of* an event — useful for slicing, never a substitute for firing the right event in the first place. Then point each campaign at the step it is actually buying: acquisition campaigns at the entry step, monetisation campaigns at the paid step. **Keep a broad union event firing alongside during migration** so live campaigns do not lose signal while the new events accumulate history. Retire it only once the specific events have enough volume to optimise on. ## Value bidding is not the shortcut it looks like The common objection is "one event is fine, we will bid on value instead." Optimising on value needs enou