so when do you actually need your own metrics monitoring system

We've been using basic application logs and some random Grafana dashboards from Prometheus, but with our system growing, it's getting tougher to see the big picture of how everything's doing. We have so many services now, and trying to link problems between them is a real headache. When did you realize your current monitoring wasn't enough and decide to get a more specialized metrics platform? What were the main problems that finally made you switch?