What if we were to model a typical software development lifecycle in code?

1. Breaking it down into small parts that are more approachable for solving, and also give us a steady sense of progress.
2. Priorise: ship the most valuable parts first and perhaps discard some low priority slices.
3. Over its life, it gathers context about various things.
4. Solving: define acceptance criteria then solve until we meet them
5. Verifying

When is a unit considered done? When the slice has been served. When it’s in the hands of the user, in production, potentially behind a feature flag.

Kent Beck's writing about measuring developer productivity:

Be suspicious of anyone claiming to measure developer productivity. Ask who is asking & why. Ask them what unit they are measuring & how those units are connected to profit.

I am 100% pro-accountability. Weekly delivery of customer-appreciated value is the best accountability, the most aligned, the least distorting.