There are also diminishing marginal returns of optimizing for a certain metric. The first big steps are relatively easy, and produce a good return on the invest

There are also diminishing marginal returns of optimizing for a certain metric. The first big steps are relatively easy, and produce a good return on the investment, but as you get deeper into the optimization, the costs of getting that next little bit go up. And people are tempted to cheat, and take short cuts to meet the goal. For example, getting from one nine of uptime to two nines isn't all that hard or expensive (a month of downtime per year to half a week). Getting from three nines to four nines is a lot harder, and a lot more expensive, and if you tie success at the organization to that improvement, people will fudge to reach it. Nearly every metric is like that. Amount of sales, tail latency, recruiting efficacy.