Deming had a name for adjusting a steady process in response to noise: tampering. He demonstrated it with his funnel experiment, in which people try to hit a target by moving the funnel after each drop, and scatter the drops wider than if they’d left it alone Reported.

Why reacting makes it worse

The arithmetic is simple. Suppose each week lands on the true average plus some random error. If you leave the process alone, the weeks scatter with that error’s spread. If you “correct” each week by the amount it missed last time, every result now carries two errors: this week’s, and the reversal of last week’s. The spread of results doubles in variance, about 41% wider in the units you see Derived. The team that responds to every dip isn’t steering. It’s shaking the wheel.

Responding to every dip isn’t steering. It’s shaking the wheel.

The flow rewrite habit

Picture a welcome flow that converts about 6% of new subscribers, week in, week out, with ordinary wobble. One week it shows 5.1%. Someone rewrites the second email. The next week it’s back to 6.2%, and the rewrite gets the credit. A month later another dip, another rewrite. After a year the flow has had eight versions, nobody knows which one was best, and the flow is exactly as good as it was, with more variation and a longer change log.

Each rewrite has costs that don’t show on the chart: the hours, the review cycle, the risk of a broken link or a wrong discount code, and the loss of any clean comparison. Worse, the regression you’ll meet in the next chapter makes the habit self-reinforcing. A bad week is usually followed by a better one, so the fix always seems to work.

The overtrading parallel

Brad Barber and Terrance Odean studied 66,465 households with accounts at a large discount broker from 1991 to 1996. The fifth of households that traded most earned 11.4% a year after costs; the market returned 17.9%. The average household turned over 75% of its portfolio a year Published. In a follow-up on more than 35,000 households, men traded 45% more than women, and trading cut their net returns by 2.65 percentage points a year, against 1.72 for women Published. Their explanation was overconfidence: people who trade most are surest that they know what the next move will be.

A store isn’t a portfolio, and a flow rewrite isn’t a stock trade. But the mechanism carries over. Each action feels informed, has a small cost, and responds to movement that’s mostly noise. Added up, the activity costs more than it earns. The operator who rewrites the flow every month is trading on noise and paying the commission in hours and in lost learning.

When to change something

• On a signal. A point outside the limits or a run means something changed. Find out what before you change anything back: a broken discount code, a tracking change or a stock-out is a cause to fix, not a copy problem.
• On a plan. If a steady process is steadily not good enough, the whole system needs a deliberate change: a new offer, a new sequence, a new page. Make it once, with a holdout if you can (see The Honest Test), write down what result you expect, and watch the chart for the shift.
• Never on a normal week. A normal bad week is the process doing what it does.

Do this

• Pull the change log for your top five flows and count the edits in the last six months. For each, mark whether it followed a signal, a plan, or a bad week. Freeze any flow with more than two bad-week edits for the next quarter.