Forced answering (FA) is a frequent answer format in online surveys that forces respondents to answer each question in order to proceed through the questionnaire. The underlying rationale is to decrease the amount of missing data. Despite its popularity, empirical research on the impact of FA on respondents’ answering behavior is scarce and has generated mixed findings. In fact, some quasi-experimental studies showed that FA has detrimental consequences such as increased survey dropout rates and faking behavior. Notably, a theoretical psychological process driving these effects has hitherto not been identified. Therefore, the aim of the present study was twofold: First, we sought to experimentally replicate detrimental effects of FA on online questionnaire data quality. Second, we tried to uncover an explanatory psychological mechanism. Specifically, we hypothesized that FA effects are mediated through reactance. Zero-order effects showed that FA increased state reactance and questionnaire dropout as well as reduced answer length in open-ended questions. Results of survival and mediation analyses corroborate negative FA effects on data quality and the proposed psychological process.