Chesterton's Fence

Chesterton's full idea: if you come across a fence in the middle of a field with no obvious purpose, the instinct is to tear it down. The sensible rule is not to touch it until you've worked out why it's there — because somebody put it there for a reason that isn't currently visible to you.

When you join a new product area, especially a regulated one, you'll find dozens of strange-looking legacy processes, hard limits, seemingly pointless extra steps, and rules that 'don't make sense'. Usually there's a reason: an old outage that took down the business for six hours, a stern letter from a regulator, a customer complaint that left scars on a whole department, a near-miss with a data breach.

Find the reason first. Then decide whether the reason still applies. Then decide whether to remove the fence. Skipping straight to removal is one of the most common career-shortening mistakes a new PM can make.

The 72-hour cooling-off rule. A PM joins the payments team and notices there's a 72-hour cooling-off period on deposits over £10,000 before the funds can be traded. Customers complain about it constantly on review sites. The PM's instinct, three weeks in: 'this is obviously terrible UX, let's kill it.' They write a proposal. A senior engineer on the team, seeing the draft, gently points them at a 2019 email chain. The 72-hour period is there because it was required by a specific FCA supervisory letter following an incident in which a customer deposited stolen funds and traded them out within 4 hours, making recovery impossible. The fence is literally in a regulator's letter in a shared drive. Removing it wasn't 'improving UX'; it was about to be a career-limiting move. The senior engineer saved the PM's quarter in an eight-minute Slack message.

Coca-Cola and New Coke, 1985. The most famous Chesterton's Fence disaster is Coca-Cola's 1985 launch of New Coke. Blind taste tests showed the new formula beat both Pepsi and classic Coke, and Coca-Cola had genuine data on its side. What the data missed was the fence: classic Coke wasn't a beverage, it was a cultural artefact, and the 'rule' being torn down was 'don't mess with things people love even when the numbers say you can'. Within 77 days, under customer rebellion, Coca-Cola Classic was back on shelves — a reminder that fences in consumer products are sometimes made of emotion rather than regulation, but they're just as load-bearing.