Behaviour
A witness makes a plan harder to abandon
Telling one person what you intend to do changes the cost of quietly not doing it. That is the whole mechanism, and it works.
There is a settled way of talking about commitment devices. It is worth asking how much of it survives contact with the detail.
The argument in brief
- A plan nobody knows about can be revised without it feeling like a revision.
- The witness supplies memory, not judgement, so expertise is irrelevant.
- A commitment with no stated way to change it gets broken rather than adjusted.
Why a private plan is fragile
A plan nobody else knows about can be revised silently, and a revision nobody witnesses never quite feels like a broken commitment. The revision usually arrives with a reason that seems compelling at the time and reads rather thin a year later. Because nothing external changed, no record survives showing that the plan was ever different from what you are now doing.
This is how people end up with portfolios they never chose, through a sequence of individually reasonable adjustments. The absence of a witness is not the only cause, but it removes one of the very few frictions available.
What a witness actually does
Telling somebody your intended contribution rate and allocation attaches a small social cost to changing them without explanation. That cost is enough to make you articulate a reason, and articulating a reason is where most impulses quietly fall apart. The witness needs no investing knowledge at all, because their function here is memory rather than judgement.
A partner, a sibling or a friend who will ask about it once a year is entirely sufficient for the mechanism to work. The effect is documented across many domains where people commit publicly to a behaviour, though its size varies with context.
Written commitments to yourself
A dated document stating what you will do and under what conditions functions as a witness when no person is available. The date matters, because it establishes that the intention preceded the market conditions you are now reacting to. Rereading it before any change converts a decision into a comparison against something specific and previously agreed.
The useful part is this: the document is most useful when it names conditions rather than intentions, since conditions are checkable and intentions are not. Keeping it somewhere you will actually find it again is a surprisingly common point of failure.
Where commitment devices go wrong
A commitment that is too rigid gets broken entirely rather than adjusted, and a broken plan is usually replaced by nothing. Building in a stated procedure for changing the plan is what keeps it alive when circumstances genuinely change. That procedure should include a delay, because the changes worth making survive a fortnight and the impulses reliably do not.
Where it helps most, commitments involving locking money away carry costs that only become clear when circumstances change unexpectedly.
The aim is to raise the cost of an impulsive change, not to make any change impossible to execute.
Choosing the right witness
The best witness is somebody who will remember and ask, not somebody who will offer opinions about your individual holdings. A witness who trades actively will tend to pull the plan towards their own behaviour without ever intending to. Sharing the process rather than the balances keeps the conversation about whether you did what you said you would.
For couples the plan being joint means the witness is built in, provided both people were involved in writing it. Where money is already a source of tension, this needs handling carefully rather than becoming a form of monitoring.
Some of this will suit you and some will not, and that is the point.
The annual conversation
Once a year, tell your witness whether you did what you said and what, if anything, you changed. That conversation takes a few minutes and constitutes the entire maintenance cost of the whole arrangement. Explaining a change out loud is a considerably stronger test than justifying it silently to yourself.
Put simply, most changes that survive being explained were reasonable, and most that do not survive it were reactions. This is not accountability in any formal sense; it is a small friction placed where impulses would otherwise pass unopposed.
The takeaway
Say it out loud to one person. That is most of the friction a plan needs to survive its worst year.
Pick the one that costs you least, and let the rest wait.
Questions readers ask
Does the witness need to understand investing?
No. Their job is to remember what you said and ask about it. Someone with strong opinions about holdings is usually a worse choice than someone with none.
What if my plan genuinely needs changing?
Then change it through the procedure you wrote down, which normally means a delay and a written reason. The point is to filter impulses, not to freeze the plan.
