Today Benjamin Mitchell played a small exercise I really liked during his Kanban talk.
Benjamin gave each of two people 5 A4 envelopes and 5 pieces of paper. The two people were given instructions to either write a letter sequentially, or to do it in batches.
The sequential person had to put the paper in the envelope, write their address on the front then mark an “X” for a stamp. They had to do this 5 times.
The batch person had to do each of those steps in turn; filling in 5 envelopes, writing 5 addresses and “putting on” 5 stamps.
Now, I remember another exercise which teaches us that multi-tasking is bad. If we’re asked to write all the letters of the alphabet as capitals, then write them all as small letters, then write the numbers from 1 to 26, we do this much more easily by doing the whole of one job than we do by switching between them. It’s very hard to write, “A, a, 1, B, b, 2” – much harder than it is to just write “ABCDEF…” etc. It gets even nastier if we write roman numerals too!
For that reason, I predicted that the batch job would finish more quickly. It’s not like software development, where we do different things. It should be even simpler than writing a sequence. It’s the same thing, five times.
Yet the person working sequentially – doing each letter in turn – finished a long time before the other person. The addresses looked about the same length, and the sequential worker had written his far more neatly, too! Benjamin’s reaction told us that this was pretty standard for the exercise – he expected this.
Why? What was it about this exercise that meant the person writing each letter in turn went so much faster than the one filling the letters, then writing the addresses, then the stamps?
I have a couple of ideas, but I’m curious to see what the community thinks! I’ll write the most interesting answers in an edit here… as well as the most outrageous ones. Let me know in comments, and if you try it yourself I’d love to know the results.
Edit: I said I’d write the most interesting answers here, but too many of them are interesting. I do particularly like this breakdown of the game, via Graham Lee.
Don Reinertsen’s explanation of transaction costs is also helpful:
I am a big proponent of reducing batch size, but the viability of small batches ultimately depends on transaction costs. If you ran the game with the envelopes, the letters, the writing desk, and the stamps each in separate corners of the room, or in different buildings, you would undoubtedly get a very different outcome. Reducing transaction costs enables the payoff brought by small batches.
Thank you all for your illuminating answers!