The devops handbook how to Create World-Class Agility, Reliability, & Security in Technology Organizations By Gene Kim, Jez Humble, Patrick Debois, and John Willis

Figure 11:
 Invest 20% of cycles on those that create positive, user-invisible value
(Source: “Machine Learning and Technical Debt with D. Sculley,” 
Software Engineering Daily
 podcast, 
November 17, 2015, http://softwareengineeringdaily.com/2015/11/17/
machine-learning-and-technical-debt-with-d-sculley/.)
After the near-death experience of eBay in the late 1990s, Marty Cagan, author 
of 
Inspired: How To Create Products Customers Love, 
the seminal book on product 
design and management, codified the following lesson: 
The deal [between product owners and] engineering goes like this: 
Product management takes 20% of the team’s capacity right off the 
top and gives this to engineering to spend as they see fit. They might 
use it to rewrite, re-architect, or re-factor problematic parts of the 
code base...whatever they believe is necessary to avoid ever having 
to come to the team and say, ‘we need to stop and rewrite [all our 
code].’ If you’re in really bad shape today, you might need to make 
this 30% or even more of the resources. However, I get nervous when 
I find teams that think they can get away with much less than 20%.
Cagan notes that when organizations do not pay their “20% tax,” technical 
debt will increase to the point where an organization inevitably spends all of 
its cycles paying down technical debt. At some point, the services become so 
fragile that feature delivery grinds to a halt because all the engineers are 
working on reliability issues or working around problems.
By dedicating 20% of our cycles so that Dev and Ops can create lasting counter-
measures to the problems we encounter in our daily work, we ensure that 
Promo 
- Not 
for 
distribution 
or 
sale

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technical debt doesn’t impede our ability to quickly and safely develop and 
operate our services in production. Elevating added pressure of technical debt 
from workers can also reduce levels of burnout.