What's a business metric that went sideways before anyone noticed?

Most teams I talk to don't find out a number broke from a dashboard. They find out from a customer complaint, a bad month, or someone finally opening a spreadsheet they'd been ignoring.

I'm curious how the makers here handle this. Say a conversion rate quietly drops 15%, or churn ticks up, or a location's sales dip. What actually alerts you? A tool, a weekly review, gut feel, or you just find out late like the rest of us?

A few things I'm trying to learn from this thread:

• Which metric has burned you by staying broken too long

• Whether you trust automated alerts or find them noisy

• What the first sign usually is when something's off

I ask partly because I've been building KPILIO, a tool that watches business metrics and flags the weird stuff automatically, so I'm genuinely interested in how people solve this today without something like it.

Curious what everyone's worst "we should have caught that sooner" story is.