Previous studies on newcomer socialization have evidenced quite consistently that newcomers' affective commitment tends to decline in the first years of employment. In this paper, we attempt to explain why a minority of Brazilian newcomers in a governmental organization (N = 194) display growth in commitment (33 per cent) in the first 3 years of employment, despite the fact that the odds are clearly in favor of decline (62 per cent). We reasoned that the minority displaying growing commitment may have had qualitatively different work experiences or would have different personal characteristics. We used latent growth modeling and post hoc tests to analyze the hypotheses. Concerning individual differences, newcomers with growing commitment were on average older but did not have higher work centrality. Concerning work experiences, newcomers whose training matched the job (high person–job fit) and whose tasks were challenging were more prevalent in the growing commitment group. The newcomers who showed declining commitment were more likely to feel overwhelmed by the amount of work in the new role (high role overload) and were typically not promoted to higher ranks. Change in commitment also predicted self‐reported performance (productivity and initiative) 3 years after organizational entry. Copyright © 2016 John Wiley & Sons, Ltd.