This study aims to investigate the influence of the big-5 personality traits on causation and effectuation decision-making logics using the entrepreneurial process theory. This is an empirical study based on 113 surveys of managers/entrepreneurs from the Estonian IT sector. The questionnaire was uploaded onto the online platform of connect.ee and the participants were invited to complete it. The study reveals that only conscientiousness positively and significantly predicts causation logic. However, four of the five factors of personality traits positively and significantly predict effectuation logic, i.e., openness, conscientiousness, extraversion, agreeableness, except for neuroticism. Furthermore, only nine of 25 hypotheses are positive and significant, and of the 11 relationships of the model, three are negative and non-significant for causation logic and eight are negative and non-significant for effectuation logic. Finally, there are another five relationships of the model which are positively but non-significantly related. Managers of IT companies in Estonia should think of shifting to effectuation logic as most personality traits predict effectuation logic, and therefore, there is the possibility of a better performance for IT firms. Eight of the 51 items of the model had standardised regression weights below the threshold of 0.500, but only four were extracted from the final model. The extraction of items from the model indicates the need for the re-identification of the constructs of personality traits using, for example, the six-factor personality traits.