Why do you treat some of your money as if it were less real?

Why this matters. The market sees one balance. You do not, and the accounts you keep privately determine what you are willing to risk with each.

Money set aside for one purpose is not interchangeable with money set aside for another, even when both sit in the same account and nothing distinguishes them.

The finding

Replicated: Richard Thaler's work on mental accounting (1985, and the 1999 review) established that people sort money into notional accounts and apply different rules to each — different tolerance for loss, different willingness to spend, all on money that is fungible in fact.

It is not irrationality for its own sake; the accounts do useful work in ordinary life. They do specific damage here.

What it does in a market

Three things, all of which the next lessons take one at a time:

• Money recently gained is held differently from money held a while
• The level at which an account returns to even acquires a significance no other price has
• Risk taken in one "account" is not felt against the whole

Each is a separate lesson because each has its own tell.

Why naming it helps

Mental accounts are invisible precisely because they feel like the natural shape of your money. Nobody experiences themselves as maintaining notional ledgers; they experience some money as different.

Naming the mechanism converts a feeling into a thing that can be checked.

The artefact

One statement, one column. Everything you have at risk, written in a single list, without grouping — no "long-term" section, no "play position", no separate line for the money you made last month.

Reading it as one number is uncomfortable in a way that is itself the lesson. The discomfort is the accounts objecting.

Try it now

Write everything you have at risk as one list and one total. Notice which entries you wanted to put in a separate section.