What a cactus can tell you about how your brain works

Kelly Smith
Human Parts
Published in
4 min readApr 15, 2024


Illustration of a cactus
Cactus illustration by the author

My husband rescued the limp little cactus from a supermarket display. He brought it home in a sad plastic pot with a yellow label that said “Reduced to 50p”. I repotted it into a vintage Ambleside ceramic planter with a matching saucer and put it up on a high shelf under a skylight. There it sat, green and unmoving, slowly gathering dust.

At first I assumed it was a Christmas cactus, but Christmas rolled around and it failed to flower. “Typical”, I thought. But I kept it all the same.

Life carried on. Winter came and went, slowly melting into spring. Then, a miracle: a tiny bud which burst and blossomed into a white spiky flower.

Photo of an Easter cactus
Easter cactus in bloom (photo by the author)

I posted photos of it with the caption “Christmas cactus… flowering in spring?!”. A green-fingered friend advised that it was actually an Easter cactus (Rhipsalidopsis) not a Christmas cactus (Schlumbergera). A subtle difference, but that explained its odd flowering time, and also the fact that I hadn’t killed it by forgetting to water it (Easter cacti originate from drier forests than their Christmas cousins).

Further research revealed that the Easter cactus was identifiable by its rounded leaf shape, as compared to the sharper outline of the Christmas cactus. Who knew?

Illustration showing the difference beween Christmas Cactus and Easter Cactus.

As a result of this incident I have begun to ruminate on how often my initial assumptions are mistaken. As Mary Poppins sang: “A Cover Is Not The Book” (ok, it was actually Mary Poppins Returns, but close enough).

As human beings we have a tendency to use our intuition to make rapid judgements and decisions; a mode of thinking which the psychologists Daniel Kahneman and Amos Tversky called “System 1”.

In System 1 thinking, people quickly react in an instinctive and emotional way. System 2 thinking, in contrast, is slow and logical. The unconscious System 1 instincts influence the conscious System 2 processes and the brain combines the two in order to make decisions.

A common illustration of this concept is the following puzzle:

A bat and a ball together cost £1.10. The bat costs £1 more than the ball. How much does the ball cost?

The instinctive reaction (System 1) for the majority of people is to say it’s 10p — but when rational thought (System 2) is applied it becomes obvious that the answer is 5p.

This is why, therefore, I had assumed that my bargain supermarket plant was a Christmas cactus. I made a quick judgement based on tacit knowledge and didn’t bother to look any deeper. Even when the cactus failed to flower at Christmas I still assumed it was an unhappy Christmas cactus and didn’t consider that perhaps it wasn’t a Christmas cactus at all.

To return to the main point: the core concept of intuitive System 1 thinking is accessibility — i.e. how easily information (such as the name of a plant) comes to mind. To understand intuition, therefore, we need to understand why some things come to mind more easily than others.

A large part of the answer is context — the different elements of a situation and their relationship to each other.

Kahneman demonstrated this concept in his Nobel Prize Lecture using the following diagram: what looks like a B when presented alongside letters can equally be read as 13 when presented alongside numbers.

Equally, a cactus which might be assumed to be a common Christmas cactus when purchased from a supermarket for 50p might, under different circumstances, have been recognised as a rare “Sirius” cultivar of Easter cactus.

Drawing from Kahneman’s Nobel Prize lecture showing how the letter B can equally be read as the number 13.
Example of context from Kahneman’s Nobel Prize Lecture

The issue of context and its influence on design is a broader topic for another time. For now, the main point is this: context is an illusion, and cacti doubly so. All together now: ♫ “The Cover Is Not The Book” ♫ …

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