This is Rule Cache Management concept. Pega maintains cache of rules which are invoked at least once after the server restart until next server restart. if the cache already exists for a Rule, everytime that rule is invoked, you can see Cache Hit (Found) in tracer. If a new Rule is created and if thats invoked for the first time then you can see Cache Miss for that rule. Cache miss would happen for all after server restart. EVery rule is checked in Cache first before building cache for that rule. So this avoids keeping cache for all rules in the system even though nobody is using them. This is very important for Rule resolution to quickly find the rule and it also improves overall performance of the system.