The example of a psychotherapist is one of the clearest illustrations of how surplus-value extraction works under capitalism.

A friend of mine is studying psychology and will soon become a therapist. I asked him whether he plans to open his own practice or work at a clinic. He said he prefers to open his own practice because, at a clinic, the clinic would take a portion of his earnings. For example, if a therapy session costs 200 EUR, as a self-employed therapist, he would keep the entire 200 EUR. However, if he worked at a private clinic, the clinic might take 50%, leaving him with only 100 EUR, paid indirectly through his salary.

At that moment, I pointed out that this principle applies broadly under capitalism, whenever there’s a choice between being self-employed and working for a private company. When you're self-employed, you keep all the value you produce. But when you're employed by a company, a portion of the value you create is taken by the CEO or shareholders, which Marx referred to as "surplus-value."

The psychotherapist example is particularly useful for illustrating surplus-value extraction for two reasons. First, becoming a therapist requires minimal capital—aside from perhaps renting a space for your practice—so many therapists end up being self-employed. Second, it’s easy to calculate the value a therapist generates because their work isn’t tied to any pre-existing infrastructure. If a therapy session costs 200 EUR, the therapist directly generates 200 EUR of value in that session.

To clarify this further, let’s consider my situation. I work as a software engineer, and I frequently handle change requests that my company bills at certain rates. Sometimes, I make changes that are invoiced at 1,000 EUR, but that doesn’t mean I personally generate 1,000 EUR of value in that moment. The work I do relies on a pre-existing software infrastructure that was developed before I even joined the company. For me to make a change worth 1,000 EUR, the software itself needs to exist in a specific state beforehand. This makes it difficult to measure exactly how much value I’m producing as a software engineer, since my work builds on something that was already there. In contrast, a therapist’s work is much easier to quantify, which is why I believe the example of the psychotherapist is the simplest way to explain how capitalism works to someone unfamiliar with Marxist theory.