when should you actually put circuit breakers in place

Hey everyone, I've been thinking a lot about system resilience lately. We've all had those days where downstream services go down or just get sluggish, right? I've used circuit breakers before, but I'm stuck on when to actually add them. When is it time to throw in that extra bit of complexity? Is it all about how often things fail, or should we also look at weird latency spikes, or maybe certain error types? I'd love to hear what you all have experienced and how you decide when to implement them.