Behaviour
A Rule Survives What A Judgment Call Does Not
Decisions made in advance and written down hold up under stress because they were formed by a different self than the one facing a falling market.
Two investors can hold identical portfolios and end up with different outcomes because one decided things in advance and the other decided them in the moment. The difference is procedural rather than analytical.
The conditions of a decision change its content
A choice made on a quiet weekend is made with the whole plan in view. Time horizon, contributions and the purpose of the money are all present at once.
The same choice made during a sharp fall is made under different conditions. Attention narrows to the immediate threat, and the horizon shrinks to whatever feels urgent.
Neither state is more honest. They simply weigh things differently, and the calm version is the one that had access to the full set of considerations.
A written rule converts a decision into a task
An intention held in the head is re-litigated every time it is tested. Each occasion is a fresh opportunity to reason toward a different answer.
A written rule changes what is being asked. The question stops being what should be done and becomes whether the stated condition has occurred, which is far easier to answer.
That shift matters most exactly when the reasoning is least reliable. Executing a task requires less of a stressed mind than reaching a conclusion does.
Rules make deviation visible
Without a rule there is nothing to depart from, so a change of course leaves no trace. The portfolio simply becomes something else, gradually and without any recorded moment of decision.
A written rule creates a record. Departing from it is a distinct act that has to be noticed, which introduces a small delay between the impulse and the trade.
Small delays are disproportionately useful. Many decisions that seem necessary during a volatile week seem optional a few days later.
A rule needs a trigger, not a mood
Rules fail when their conditions are vague. Anything that depends on things looking bad or markets seeming stretched has smuggled the judgment call back inside.
Workable triggers refer to observable facts: a date on the calendar, an allocation drifting past a stated band, a contribution arriving, a goal reaching a defined distance.
The trigger should also specify the action completely, including what is bought or sold and in what order, so that nothing has to be improvised at the moment of execution.
The limits of rules are worth stating
A rule is not a forecast and does not make an allocation appropriate. A badly chosen structure followed consistently is still a badly chosen structure.
Rules also need revision, which is why the sensible practice is to schedule review at a calm interval rather than to amend them during the events that test them.
What a rule contributes is narrower than it first appears. It removes the moments in which the plan is most likely to be abandoned, and those moments are where most of the damage happens.
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.
