[robflaherty]

The author's framework-"you just start small and only add one at a time as needed"-and given example illustrate exactly the process that leads to too many metrics. Pick a few metrics, add another, add another, add another. If you have 5 teams working on a product you quickly end up in the 50 metrics scenario.

Too many metrics can be a problem but it's not the real problem. The real problem is choosing metrics without any regard for the decisions they're supposed to inform.

When you understand that the purpose of all measurement in business is to reduce uncertainty for a decision to be made, everything comes into focus, and you'll have a natural constraint on your scope of measurement.

[ares2012]

That would be true if you didn't assign a cost to each metric that you add. It was when the cost of tracking metrics plummeted that this started to become a problem, as there was no external friction in collecting more. If you assign a cost, and respect that cost, you shouldn't continuously add more.