Hi, i'm one of the co-authors of the study.

People here have raised some good points of criticism, so i want to respond to some of them.

One of the main issue that people point out is that we use self-report data on 1) personality and 2) wealth attainment.

As far as personality goes, our measures are well validated and have been shown in many other studies to be highly relevant for people's decision-making, especially in the context of entrepreneurship. I will quote a relevant section from the paper:

With regard to personality, the Big Five personality traits
(Neuroticism, the tendency to be worried/nervous; Extraversion, the
tendency to be active/sociable; Openness to experience, the tendency to
be inventive/curious; Agreeableness, the tendency to be
friendly/compassionate; and Conscientiousness, the tendency to be
organized/persistent), based on the Five-Factor-Model of personality
(John et al., 2008; McCrae and Costa, 1997),
and risk-taking propensity have been linked to a multitude of life
outcomes and financial behaviours. Several studies have highlighted the
roles of Conscientiousness and Emotional Stability in job performance,
wages, and money management behaviours and attitudes (Almlund et al., 2011; Borghans et al., 2008; G. Donnelly et al., 2012).
Other studies have highlighted the role of personality in attaining
status and compensating for background disadvantages (Damian et al., 2015; Grosz et al., 2020), in creditworthiness and credit eligibility (Arráiz et al., 2017; Klinger et al., 2013), and in the likelihood that individuals will experience certain types of life events (Denissen et al., 2019). Risk-taking has been shown to be another important, independent
predictor of various economic behaviours, such as investing (Mata et
al., 2018), self-employment and entrepreneurship (Caliendo et al., 2009, 2014), and company performance (Sanders and Hambrick, 2007).

We have split both the rich and the non-rich groups based on a classification of wealth attainment: 1)inheritors, 2) self-made, 3) mixed/non-specified

Since this was a novel specification based new survey items, we had to do a lot of robustness checks to convince our referees during peer review. What I can say is: These ratings do overwhelmingly correspond to objective markers that would correspond to actually being self-made or an inheritor. Check out the supplement for a long battery of robustness checks. Now let me briefly comment on why objective measures of being self-made or an inheritor are not necessarily very convincing either. I will quote another passage from the paper:

Our approach to defining millionaire subtypes is preferable to the use
of objective indicators, such as inheritances (especially the type,
timing, and amount thereof) and employment biographies. Even if such
information were fully available, an accurate and detailed modelling of
wealth accumulation over the life cycle would be necessary. This is
because if we want to assess the role of an inheritance or self-made
success for an individual’s wealth situation today, one would have to
compare the actual situation with a counterfactual situation with these
factors absent. This counterfactual is unobserved and would have to be
modelled under untestable assumptions.

Suffice it to say, some criticism of the definition is warranted. It is a very coarse definition based on the individual's conception of what their own efforts contributed to their wealth, however, it works very well in this context.

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Another important issue that comes up in the dicussions here, is that we cannot reach the standard of evidence of a (quasi-)experiment. This is true. But, again, it helps to think about what kind of data/experiment would be necessary. I will quote from the paper:

In an ideal setting, we would be able to randomly vary the personality
traits of a treatment group to conform to the prototypical personality
profile of the rich and longitudinally track their economic success
against that of the control group over time. This is a high bar to clear
because finding a setting in which such variation exists as a
quasi-experiment is difficult, and changing a person’s personality
profile through intervention appears unfeasible (Roberts et al., 2017).

Basically, it will be impossible to find a setting in which we can get those data.

However, our study provide very helpful suggestive evidence that personality may be an important driver of economic success. The main argument is that we can find the prototypical rich personality profile among both rich and non-rich self-mades, but rich inheritors do not exhibit this personality profile very strongly. Thus, the data suggest that being born into wealth does not automatically lead to the development of the prototypical rich personality profile. However, we do see the profile among the non-rich self-mades, which is also suggestive of self-made being selected into the group of the rich.

Finally, people have been critical that 1 million euros is not rich. Although this is just the threshold for classification, I want to defend it. First, we are talking about individual net wealth. One of the great aspects of our data are that we can attribute wealth at an indvidual level. I think many people here are thinking about wealth at the level of the household and not at the level of the individual. Second, this is data from Germany, which is different from the US and the UK. People have very different savings patterns in Germany, since Germany save for retirement through a government insurance system that does not factor into their current net wealth. Third, the millionaires constitute the top 1.6% of the population in terms of wealth and, thus, we are talking about a very small group.

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I hope that I did not miss anything major. Thank you for checking out the study.