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Discretionary vs. Quant - a thought experiment.

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Are there things that experienced discretionary investors are fundamentally better at understanding and applying than purely quantitative managers? In this post, we look at this question from a new and unfamiliar perspective.

Philosopher and Instagrammer Jonny Thomson describes an interesting thought experiment in his article "Inside Mary's Room: Is A Physical World All There Is?" [1] It is already about 40 years old and comes from the Australian philosophy professor Frank Cameron Jackson, who called it "What Mary Didn't Know".

Black and white + red

Thomson describes it as follows: Let's imagine a neuroscientist named Mary who lives in a completely black and white world. She is highly intelligent and has books and a computer at her disposal. She spends her days learning everything there is to learn about the colour red. She knows the science of light waves and where red is in the electromagnetic spectrum, how the eye receives light and how information is transmitted to the brain. She knows all about the part of the brain that interprets the colour red. But that's not all. She also knows all the associations associated with it, like war, love and danger. She reads about red things like strawberries, a Mediterranean sunset and blood. In short, Mary knows all the physical facts and everything else there is to know about the colour red.

But she has never seen it herself, this red.

What Mary did not know

Now imagine that one day Mary is released from her black and white world - and sees a red rose. The question now is: Does Mary learn something new from this? Does seeing red expand her understanding of colour? Does she feel something that she could not possibly have felt before?

If we assume that she is indeed learning something new, then this means that the world cannot be fully represented by material facts or descriptions. It means, as Jonny Thomson writes, that there is more to life than the physical world: there is our sense of something, or what philosophers call "qualia", our phenomenal consciousness. This refers to the subjective experiential content of a mental state that is related to the triggering physiological stimuli - for example, the experience of colour, which is not a material state. [2, 3] Or formulated differently: There is more behind concepts such as red, sadness and love than can ever be experienced through theoretical study.

Theory vs. practice

The whole thing can be extended, of course. Can one learn what it is like to be in love from all the books, records and conversations of lovers? Or learn what it is like to be at war by studying all the facts and reports about wars?

Can one learn what it feels like to invest in the stock market by evaluating all available information and correlations? Does this really teach you how it feels to experience a crash, to achieve high price gains or to endure the wildest fluctuations in cryptocurrencies?

Ultimately, it is precisely these subjective experiences, both positive and negative, that shape the actual actions of many people and will do so for years to come. Be it telecom shareholders who are still sitting on the losses from the bubble more than 20 years ago or young, naïve speculators who invest in meme stocks like GameStop without batting an eyelid.

Discretionary vs. quant

The thought experiment ultimately questions whether the universe can actually be completely reduced to physical descriptions. If that were the case, quantitative trading strategies would have to be superior to discretionary approaches. On the other hand, those who assume that certain details defy an exact description by rules and laws can use this to justify why experienced professionals can certainly perform better than quant managers. This is especially true when surprises happen - and they are more frequent in the markets. Discretionary managers can then flexibly apply their existing experience to new conditions. But will a machine ever be able to teach itself this complex skill?

Subjective experience

So where do things stand now, almost 40 years after the publication of Mary's Room? Jonny Thomson writes that Jackson ironically rejected his argument at the time . So he no longer thinks Mary learns anything new about the world by leaving her black and white past. Instead, however, he thinks she learns something new about herself by experiencing the colour red. This is exactly what describes her subjective experience.

We also experience this effect regularly in the stock market: In truth, we learn nothing new about the world, but about ourselves. But does subjective experience fit into an otherwise physically describable world? Jackson believes so: if we could reproduce all the neurobiology and behaviour associated with the colour red - which we can't at the moment - it would also be possible to reproduce the same qualia. We would all experience the same colour. [1]

Applied to the stock market, this means that if you could quantify all human thought processes and behaviours - even the bad ones - algorithms would also arrive at exactly the same decisions as discretionary investors. The world of completely objective physics would thus be saved.

If we assume that everything can ultimately be described in physical terms, can we ever make sense of subjective emotions in this world or fully understand them from a scientific standpoint?


The thought experiment revolves around a sticking point between the otherwise widely divergent sciences of philosophy and physics: if we assume that everything can ultimately be described in physical terms, can we ever make sense of subjective emotions in this world or fully understand them from a scientific standpoint? Or will there always be something that distinguishes us as human beings from the sum of all objective information? So do experiences and feelings teach us something that we can never learn from books, films or conversations? Are there things that experienced, discretionary investors can understand and apply better than purely quantitative managers? The sober, objective answer to this is "no", but the subjective one is "yes".

What the thought experiment shows is that there is a huge gap between the way the world is described and the way we perceive it. The question is whether this gap can be bridged. Jonny Thomson comes to the conclusion that the world cannot be completely reduced to physical relationships. He writes that something special and unique happens when we experience things subjectively rather than just learning about them theoretically. According to this, even the largest encyclopaedia in the universe, created by an "intergalactic superintelligent AI", will always lack one thing: What it means to have a human experience.

[1] Thomson, J., Inside Mary's Room: Is A Physical World All There Is?, accessed 08.12.2021,
[2] Wikipedia, Frank Cameron Jackson, accessed 08.12.2021,
[3] Wikipedia, Qualia, accessed 08.12.2021,

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