The 9x Effect

What it is

Two parties look at the same switch and neither of them sees it clearly.

The incumbent user is standing on one side. They have a keyboard they can type on, a bank they can log into, a spreadsheet whose quirks they have memorised. Whatever it costs to leave is a cost they will pay now, and whatever the new thing offers is a benefit they will receive later, if the new thing works. Gourville's estimate is that this loads the incumbent by about three to one.

The builder is standing on the other side, and has the mirror-image problem. They have spent two years on the new thing, know exactly what is better about it, and can list nine improvements without pausing. Their estimate of what those improvements are worth is inflated by roughly the same factor, and in the opposite direction.

Multiply three by three and the gap the challenger has to clear is nine. That is the whole derivation, and it is worth being blunt that this is what it is: two rules of thumb multiplied together to produce a third rule of thumb. Gourville is not reporting an experiment in which nine was measured. He is combining two estimated biases into an estimated threshold, and the number's usefulness is as a corrective to a product team's optimism rather than as a quantity anyone should plan against.

The psychology under the first half is well documented even though the multiplier is not. Switching is felt as a loss before it delivers any gain, which is loss aversion operating on possession rather than on money, and it is the same mechanism prospect theory describes when it says outcomes are judged from a reference point rather than in absolute terms. A user's reference point is the product they already use. The competitor's improvement is a gain measured from there, and the effort of moving is a loss measured from there, and losses on that curve are steeper. Nothing in that account requires the number three.

Eyal's use of the rule in Hooked is strategic rather than psychological. He deploys it to argue that a habit is a commercial moat: a product people already reach for automatically is not merely liked, it is economically defended, because a rival now has to overcome inertia as well as build a better product. That is the commercially interesting reading, and it is why the concept sits in a book about building habit-forming products rather than in a book about consumer bias.

This page is tagged unreviewed, and in this case the tag is doing real work. The vault's note is definitional, its only source is Hooked at pages 22 to 23, and the vault's own audit of that book warns that Eyal repeatedly gives a finding and a number without naming the researcher, institution or year in the visible text. The attribution to Gourville is recorded at medium confidence, the year 2006 with it. Nobody here has read Gourville. Take the two threefold multipliers and the nine as his estimates as reported by Eyal, and do not put them in a sentence beginning "research shows".

In effect

The mugs, where a threefold gap was actually measured

The closest thing to a measurement in this neighbourhood is not Gourville's. Kahneman, Knetsch and Thaler gave people a mug and asked what they would sell it for, and asked a second group simply to choose between the same mug and cash. Sellers named $7.00 to $7.12. Choosers valued it at $3.12 to $3.50. That gap is roughly two to one, not three to one, and Tversky and Kahneman used it in 1991 to derive a loss-aversion coefficient they described as slightly greater than two. It is the best evidence that the first of Gourville's two multipliers is measuring something real. It is also, unhelpfully for anyone wanting a tidy number, the paradigm that David Gal and Derek Rucker single out in 2018 as the one most sensitive to how the question is asked.

QWERTY, and the keyboard nobody switched to

The stock example is the Dvorak layout, which is more efficient than QWERTY on the arrangement of its keys and which has never displaced it, including among people who type for a living and would benefit. Eyal offers it as the case of habit strength beating measurable product quality outright. Two cautions. The vault's source for Dvorak being the better layout is Eyal asserting it, with no measurement traced behind the assertion, and the QWERTY story is old enough and repeated often enough in business writing that it has become an emblem rather than a case study. What it illustrates cleanly is the shape of the problem: a switching cost paid entirely by the individual, against a benefit that only arrives after the retraining.

The habit as a moat

The product-design use is the one Eyal actually wants. If displacing an established behaviour requires a ninefold advantage, then a company that has got a user into a routine has bought itself an enormous margin for error, and can ship a worse product than its challenger for years without losing. That is the argument behind treating habit formation as a strategy rather than a by-product, and it is why the same book spends its length on triggers, variable rewards and investment. See the book page for the reliability audit of what else it claims. The Habit Zone, Vitamins versus Painkillers, the Investment Phase and Stored Value are the neighbouring pieces of that argument and have no page on this site yet.

What it does not say

It does not say that nine is a measured quantity. It is three multiplied by three, and both threes are estimates. A product team using this as a planning input has adopted a heuristic, which is a legitimate thing to do, and should not describe the result as a finding.

It does not say better products lose. It says an advantage below the threshold is not felt as an advantage by the person who would have to move. Above it, products displace incumbents regularly, which is why anyone reading this has changed phone, bank or messaging app at least once.

It has not been verified here. The vault has not opened Gourville's paper, records the attribution at medium confidence, and holds the whole concept through a trade book whose audit specifically flags unattributed numbers as its characteristic weakness. Two of this vault's Hooked-derived notes have already had to be repaired for exactly that reason. This one has not been checked, and the page says so rather than implying it has.

It does not explain why anyone switches. The account is entirely about resistance. What overcomes the resistance, a broken incumbent, a social cascade, a change of context that resets the reference point, is not in the model, and that is the half a product team actually needs.

Who developed it

John Gourville, credited in the vault with the rule and the year 2006 at medium confidence. The attribution reaches us through Nir Eyal's Hooked, pages 22 to 23, rather than from Gourville's own publication, which nobody here has read. Gourville has no page on this site. Nir Eyal, who imported the rule and gave it its circulation among product teams, does.

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