Tuesday, September 13, 2011
You have a stack of, say, a hundred letters and envelopes to mail. You must process these by hand. Is it faster to do each step of the process for all the letters before progressing to the next step (again, for all the letters), or is it faster to everything for each letter, one letter at a time?
The answer may surprise you:
Why does stuffing one envelope at a time get the job done faster even though it seems like it would be slower? Because our intuition doesn't take into account the extra time required to sort, stack, and move around the large piles of half- complete envelopes when it's done the other way. It seems more efficient to repeat the same task over and over, in part because we expect that we will get better at this simple task the more we do it. Unfortunately, in process-oriented work like this, individual performance is not nearly as important as the overall performance of the system.Another writer elaborates further, in response to people who were skeptical of this claim:
The shorter stuff and seal times, though, are due to the fact that you are already holding the item from the previous step. You gain 1 second each time from not having to find and pick it up...Returning to the first post, there are other advantages that have nothing to do with the efficiency of the process:
You lose between 2 and 5 seconds every time you move the pile around between steps. Also, you have to manage the pile several times during a task, something you don't have to do nearly as much with [one piece flow]...
[I]magine that the letters didn't fit in the envelopes. With the large- batch approach, we wouldn't find that out until nearly the end. With small batches, we'd know almost immediately.There are other advantages to doing work in small batches that apply even for processes that are, or can be, automated:
All these issues are visible in a process as simple as stuffing envelopes, but they are of real and much greater consequence in the work of every company, large or small. What if it turns out that the customers have decided they don't want the product? Which process would allow a company to find this out sooner?This last point is impressive, and it reminds me of how an engineer once solved a challenging problem by learning how to "fail faster".
Lean manufacturers such as Toyota discovered the benefits of small batches decades ago. When I teach entrepreneurs this method, I often begin with stories about manufacturing. Before long, I can see the questioning looks: what does this have to do with my startup?
But the theory that is the foundation of Toyota's success can be used to dramatically improve the speed at which startups find validated learning.
I have to admit that I was highly skeptical that stuffing one envelope at a time could outpace batch processing, but I suspect that it was my passing acquaintance with the great advantages automated manufacturing can offer in terms of time savings. It is interesting to learn that batch processing not only doesn't always save time, but has other disadvantages.
This post is a reminder that our thinking about even simple things like stuffing an envelope can be limited by implicitly-held premises or assumptions. Checking against reality can very easily refute one's "wisdom," and discovering why one was wrong can both correct and lead to new knowledge, including about matters that are not obviously related to one's original query.