As a leader you should be able to describe, vividly, what success looks like.

This isn’t a number. This is how it FEELS to achieve this.

Will there be less stress?

Will this make the day go faster?

Fewer complaints?

What is the pain point that gets nullified?

Think of this as the WHY of the MGR.

Next level this, have it printed to share with the team so that there is no confusion of the key performance indicators. Speaking of the plural there, I would suggest keeping to one per month until you have a few months (6 or more) of success.