Why standards should change

From Mary and John Poppendieck's article Train Wreck Management, Taiichi Ohno, a pioneer of lean manufacturing, explains why standards should change:

There is something called standard work, but standards should be changed constantly. Instead, if you think of the standard as the best you can do, it's all over. The standard work is only a baseline for doing further kaizen. It is kai-aku [change for the worse] if things get worse than now, and it is kaizen [change for the better] if things get better than now. Standards are set arbitrarily by humans, so how can they not change?

When creating Standard Work, it will be difficult to establish a standard if you are trying to achieve 'the best way.' This is a big mistake. Document exactly what you are doing now. If you make it better than it is now, it is kaizen. If not, and you establish the best possible way, the motivation for kaizen will be gone.