Easy answers might be “5S because it’s foundational to so many things” or problem solving as a good catch-all. It seems we couldn’t go wrong with respect for humanity. We could cheat and say “continuous improvement” since that leaves the toolbox open. But this is a difficult question to answer for a few reasons.
First, getting sustained benefits from any single Lean behavior or tools set requires support from other Lean behaviors. For example, quick changeover may open up capacity and/or reduce lot sizes, but the benefits are short-lived unless we visualize and audit standards, train all new people in the standards, coordinate sales inventory and operations planning, and avoid introducing new products and machines that worsen changeover times. One could argue that this is all within scope of mature quick changeover activity. It requires organizations to adopt Lean behaviors such as standard work, visual management, design for manufacturing and so forth. It requires more than only one.
Second, adopting some behaviors, tools and skill sets single may not be a viable approach. Lean management is a set of systems. Many of these sub-systems of Lean don’t function at all unless practiced as a set. The andon system is a good example. If we are lucky and living in the simplest of worlds, we can adopt andons by using red and green flags to “see problem, solve problem”.
In most cases it requires structuring smaller teams and reasonable spans of control for leaders, documenting standard work, putting in place visual controls, setting time and condition-based escalation triggers, engaging leaders in go-see routines, securing problem containment resources, developing root cause analysis capability and so forth. Should we choose “only one” Lean behavior of addressing problems quickly, this requires adopting multiple behaviors and tools.
Third, organizations are in different places and have different needs. Some may be forward-thinking organizations and ready to try anything, while others traditional and ready for only baby steps. Some organizations will have urgent needs for Lean to deliver business results, while others may have more breathing room to build for the long-term. Beginners can benefit from adopting almost any part of Lean while more advanced organizations may be stuck, unsure how to get to the next level.
If I had to choose only one Lean skill set for an organization to adopt, it would be what we call GTS or grasping the situation. This is an early step, if not the very first, in many Lean activities such as value stream mapping, Toyota kata, practical problem solving, hoshin kanri etc. Understanding our current condition requires some frame of reference such as a target condition. Where are we, in relation to where we want to be? Success at grasping the situation yield a gap, calls us to act.
Grasping the situation requires comfort with facing the truth, ability to work with facts and data, and understanding of variation as well as how human perception introduces bias. Grasping the situation requires go see and humble inquiry. It involves breaking down the complex into its simpler components and seeing things clearly. It’s harder than it sounds.
There’s one downside to GTS. It’s boring. There’s nothing flashy about understanding the current situation. The activity itself doesn’t improve anything, other than our perceived understanding. It may feel like we’re getting no return for our effort from this Lean behavior. Getting a solid grasp on reality might even make us feel worse about our situation. What’s also tricky is that we don’t truly know whether we’ve succeeded at grasping the current situation. We can always take a deeper look, uncover hidden assumptions and gain insights from broader sample sizes.
Doing one thing at a time paced by smoothed customer pull is a fundamental design principle of Lean operations. Ironically, adopting only one Lean behavior or tool at a time may not be advisable when building such a system.