Human's decision making is not necessarily always planned; their unplanned behaviour-determined by natural personality traits-also contributes to the decision making process. In this study, we investigate factors related to planned and unplanned behaviour to understand why people share political content in online social media. Based on an online survey of 257 social media users, our results demonstrate that the factors representing both planned (i.e., perceived social recognition and altruistic motivation) and unplanned behaviour (i.e., extroversion and impulsiveness) affect people's political content sharing behaviour. Our study also identifies that sharing political content is not like sharing other forms of content such as tourist attractions-the former can provoke serious punishment in some countries. Accordingly, trait impulsiveness is negatively associated with political content sharing behaviour. We also found that collective opinion moderates people's planned behaviour, but not their unplanned behaviour. In other words, personality traits are unaffected by others' opinions, but traits that humans can control can be shaped by others'.