This week we tackle Chapter 4 of Tame your Work Flow, The chapter is titled “Utility of Flawed Mental Models.” The goal of the chapter is to make sure we understand why reducing wait time makes sense and why that reduction has an impact on delivery.
The premise of the chapter is set up with the statement:
According to Little’s Law, as the Flow Time at the denominator is decreased Throughput will increase. The contradiction here is that – from a Theory of Constraints (ToC) perspective – a system simply cannot deliver any more Throughput than its Constraint. Since we have not reduced Touch Time, the Constraint cannot have increased its Capacity in any way.
The authors point out that the two models at the heart of the book seem to conflict at a very basic level. Using the paradigm of the ToC would push us to find the constraint, exploit (use it to its fullest capacity) and then to elevate (increase the capacity). These types of changes would generate a focus on touch time (changing how we do the work). Daniel and Steve use a set of mental experiments to show how starting with getting rid of wait time generates improved throughput without substantial investment and creates a stable environment of making touch time changes later.
Attacking wait time does not directly impact throughput because it has no direct effect on the constraint. The question then is why does throughput apparently improve when we improve flow efficiency by removing wait time. On page 72, the authors state, “When Flow Efficiency is low, the system ordinarily performs at a rate that is less than that of the nominal Capacity of the Constraint.” This is really the crux of why reducing wait time has an impact. Simply put, the constraint is underutilized — it has spare capacity.
In the mental experiments in the book, Daniel and Steve show how reducing wait time squeezes out multitasking which reduces the context switching, and unneeded coordination and synchronization which uses up the spare captivity of the constraint yielding more output. This is exploiting the constraint, even though, at least at this point, we have spent no time trying to identify the constraint. As we noted in Chapter 3, reducing wait time does not require any substantial investments in changing how work is done, improved tools, or investment in additional people (queue the Dire Straits song “Money for Nothing).
After we have exhausted wait time, the focus of the book shifts to touch time which means finding the constraint and jumping into the Theory of Constraints.
Catch up on previous entries
Week 1: Logistics and Front Matter – https://bit.ly/2LWJ3EY
Week 2: Prologue (The Story of Herbie) – https://bit.ly/3h4zmTi
Week 3: Explicit Mental Models – https://bit.ly/2UJUZyN
Week 4: Flow Efficiency, Little’s Law and Economic Impact – https://bit.ly/2VrIhoL
Remember to buy a copy of Tame your Work Flow to support the authors and blog!
