Having to store another copy of everything that happens for every. single. fucking. use case.
Having to shell out for yet another tool every time you want to interrogate your systems in some marginally different way, or by a different team.
And you store the information about it in how many different places?
* monitoring/metrics
* logs
* traces
* APM
* exception tracker
* B.I.
* front end metrics
*...
And you pay for it again, every time.
But that's 10-30% *total* spend. Most of these tools are priced to cost you 10-30% *each*.
But they aren't.
Because they pre-aggregate.
You can only achieve observability if you have access to raw events, so you can ask new questions at will without shipping new code.
The reverse is impossible.