I wrote a comment, and figured I might as well cross-post here. (I changed things up a little, and left out the first part.)
What I think gets to the heart of Tom’s insight about “optimizing” is the relationship between several important variables:
Capacity: how much a person can handle in a period (say, 24 hours in a day)
Throughput: how much “stuff” a person can fit into those 24 hours
Utilization (U): Throughput / Capacity, or how “busy” a person is, or how much of their time they actually use
Processing Time (T): how long it takes a person to get stuff done
Variability (V): how “routine” is a person’s life? How much unexpected stuff (work / play) comes up? How much variability is there in how long it takes a person to complete their routines (e.g., do they oversleep a lot)?
Wait Time (WT): how long does a person have to wait before starting something new (e.g., new hobby, vacation, project at work)? Said differently, how responsive can a person be? If he want to change things up, how long does it take to clear his existing schedule?
There’s a famous formula that basically measures the responsiveness of a system, called the PK formula:
WT (a.k.a. lack of responsiveness) = T * U/(1-U) * V
There are all sorts of things to read from this, but the key takeaway, I think, is that there is an unavoidable tradeoff between capacity utilization (how much a person has taken on), variability (how much a person can do unexpected things, like sleep in or go to happy hour), and responsiveness (how long before a person can start a new task).
As utilization approaches 100% (i.e., as a person get busier and busier), his ability to respond to new stuff plummets, and the time he has to wait before starting new things basically goes to infinity. Highly variable processes have the same effect.
So, in terms of “optimizing” the system, there’s a clear choice that has to be made:
- Maintain high capacity utilization while religiously sticking to routines, in order to both be productive and remain agile enough to take on new things?
- Accept that life is crazy, and trade responsiveness for the opportunity to go to sleep in whenever you feel like it?
- Or, prioritize responsiveness and agility, and limit capacity utilization so you have wiggle room to take no new things?
Obviously, a big part of this is a person’s stage of life. Having a family changes priorities – it would seem to me that responsiveness becomes the key metric, and parents take steps to reduce the variability of their lives. (No more sleeping in!)