The hole your brain papers over

Try this for a moment, it takes twenty seconds.

On a sheet of paper, put a cross on the left and a dot on the right, about ten centimetres apart. Close your left eye. Hold the paper at arm's length and look at the cross with your right eye; the dot you still catch out of the corner of your eye. Then slowly move the paper towards you.

At a certain point the dot disappears. Gone. And the strange part is not that it is gone, the strange part is that no hole is left behind. You simply see paper.

What is happening

At the spot where the optic nerve leaves your retina there are no light-sensitive cells. No information comes in there. The French natural philosopher Edme Mariotte described this in 1668, and it has been beyond dispute ever since: everyone has this hole, in every eye, always.

What you see there is not nothing. It is a guess. The visual system looks at what surrounds the hole (colour, texture, lines that continue) and delivers what ought to be there. On wood grain you see wood grain. On squared paper the squares simply carry on.

That is an achievement in itself: it happens constantly, without effort and without your asking for it. The problem lies elsewhere.

The missing package insert

The brain does not report the repair.

No little border appears, no blurred patch, no signal saying: careful, this bit is an estimate. You get the same kind of image as the rest, with the same self-evidence, with the same certainty. Perception and supplement are delivered in one package, without a label.

Were your system tidy about it, a dotted line would run around the spot. Then you would know: here I looked, and here I guessed. That is precisely what is missing, and that is precisely why it is a blind spot in two senses. You do not see the hole, and neither do you see that you are not seeing it.

The leap I am making explicitly as a leap

Now something I offer emphatically as a metaphor and not as physiology, because otherwise this becomes the kind of essay I do not believe in myself.

What your eye does with a hole in the retina resembles, in its outcome, what your mind does with a hole in the information.

A client does not respond for two weeks. That is the observation. What you are left with is: he has gone to the competition. An employee says little in the meeting. Observation: he said little. What you are left with: he disagrees. A quote does not come back. Observation: no answer. What you are left with: too expensive.

In all three cases there was a hole, something was filled in, and the filling was delivered without a label. You do not have a suspicion. You know.

And here is the limit of the comparison, because without that limit it is cheap imagery. The blind spot in the eye is one fixed, measurable, always present mechanism in the anatomy of the eye. The mind's fillings-in are a messy collection of memory, expectation, mood and language, which works differently in every situation and cannot be located in a single place. The one is a hole in an organ; the other is a habit of making meaning. They resemble one another in what they produce, not in what they are.

Whoever mistakes the image for proof is doing exactly what the image describes.

A moment to take with you: today you filled in at least one thing and had the feeling that you saw it. Which one?

What this is worth if you build

The practical gain does not lie in getting rid of the spot. That cannot be done. It lies in knowing roughly where it is, and putting something beside it.

Three things that work and that cost nothing.

With any decision that costs money or trust, write down two lines: what factually happened, and what you think it means. That is not in order to stop interpreting, you cannot do that and you should not want to. It is to put the interpretation on a line of its own, so that you find it again a month later and can check it.

Ask instead of filling in. Two weeks of silence from a client is worth a phone call, not a conclusion. The phone call costs three minutes and the conclusion costs you a month of your mood.

And have someone else look at the place where it gets expensive. Not because that other person is sharper, but because their hole sits somewhere other than yours. Two eyes see more than one, not because they are better, but because they are not blind in the same place.

That is the whole trick, and it is an old one. You do not repair your sight. You arrange a second pair of eyes at the moment it matters.