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Tesler’s law
Every application has an inherent amount of irreducible complexity. The only question is: who will have to deal with it — the user, whoever builds the application or whoever builds the platform?
Complexity does not disappear: decide whether it stays with you or with whoever uses it.
Its other name explains it better: conservation of complexity. Larry TeslerFormulated the law of conservation of complexity: it doesn’t disappear, it only changes sides, from the user to the developer, or the other way round.One reference in this work:1984The law of conservation of complexitySee in the bibliography →, who worked at Xerox PARC and at Apple, observed that every system has an amount of complexity that cannot be eliminated, only transferred. If the program does not do it, somebody does. The question the law poses is not “how to simplify”, it is who is going to pay this bill, each person who uses it, the team that builds the product, or whoever builds the platform the product is made on. A screen that is too clean is usually a screen that has pushed the work to the other side.
Why there is no neuroscience here
The biological mechanism behind the effect, and how much of it was actually measured.
Tesler is a design axiom about where to allocate complexity, and not a phenomenon with a measurable signature: the complexity inherent in a task does not disappear, so the only real decision is who pays for it, the system or whoever uses it. There is no effect to explain, hence no brain mechanism to present. What supports this law is the accumulated experience of those who build systems.
Why this law presumes no body at all
Who it was measured on, and what changes when the body on the other side is another.
Complexity does not disappear, and this law is about where it ends up. It applies equally to anyone. Whoever ends up paying the bill is usually whoever has the least repertoire and the least time to spend.
How design translates it
What to do with it on a screen, without turning a finding into a rule.
How to measure this in your product
In a financial dashboard, showing every calculation on the screen forces the person to carry each formula in their head and to decide, line by line, what matters. The alternative is to absorb the complexity into supporting algorithms, show the key results and offer the explanation on demand, for whoever wants to check. Email is the everyday example: however much an email client is redesigned, somebody has to say who it goes to and what it says. That part does not compress, and it is only the rest of the screen that can be got out of the way.
Where it breaks
Where the law does not hold, holds less, or holds in reverse.
Absorbing too much complexity also breaks. When the system decides everything, whoever uses it loses the ability to check and to correct, and comes to depend on the system getting it right, with no way to audit it.
Um caso
A real product where this showed up, with what happened and where to check it.
The three boxes that held back US$894 million
S.D.N.Y. · ruling of 16 February 2021 (Flexcube interface, Oracle) · Uso editorial
In August 2020 Citibank wanted to pay about US$7.8 million in interest to the lenders on a Revlon loan. In the system the operation used, any payment goes out as a transfer unless the operator overrides that default, and to hold back the principal three cryptically named fields had to be ticked. The operator ticked one. The reviewer and the approver agreed that was enough. The final screen warned that the funds would leave the bank and asked whether to continue, without saying how much. US$893,944,008.52 went out on top of the interest. The complexity of not sending the money stayed entirely with those operating it, and three experienced people made the same mistake, which is what the law predicts when the system absorbs nothing. The first court ruling, in 2021, let the lenders keep the roughly US$500 million they refused to return; the appeals court reversed it in 2022 and the bank recovered the money.
In re Citibank August 11, 2020 Wire Transfers, S.D.N.Y., 2021
Experimente
A piece to check in your own body what the text has just claimed.
How far complexity can be removed
Tesler’s law says every system has an amount of complexity that cannot be eliminated, and here the part of the system is played by the sentence below. Click any word or expression to remove it, and again to put it back. The traffic light beside it says whether the sentence still makes sense, has lost information, or has stopped working.
Makes sense
The sentence still says everything it said.
Now hold on to the principal
The screen from the case, reduced. You want to pay only the interest and keep the principal. Tick whatever is needed and confirm.
| Componente | Override the default instruction |
|---|---|
| FRONT | |
| FUND | |
| PRINCIPAL |
Account used is Wire Account and Funds will be sent out of the bank. Do you want to continue?
Every system has a core of complexity that cannot be eliminated, only moved. What you took out before the red did not vanish: it became work for whoever reads.
Fontes
Enunciado citado de Tesler, 1984.
- TESLER, L. The law of conservation of complexity. c. 1984. Source
Leitura complementar: Tesler’s Law Laws of UX em inglês