What motivates people to share and create content online? In real time, we linked each of N= 2, 762 individual posts (retweets and newly created content) with the self-reported motives from a sample of N= 137 highly active US Twitter users over the course of one week. We also captured their total activity of N= 48, 419 posts over 10 weeks (March-May 2022). Our results reveal that sharing (retweeting) political content stemmed mostly from motives related to expression and identity. When creating content, participants were more likely to be motivated by the goals of informing and persuading others, for which they used negative language and expressed outrage. In contrast, entertaining content and positive language was used for socializing and attention. Original and political content featuring outrage and anger was more likely to be subsequently retweeted by others. These findings may denote adaptive strategies in the incentive structure of social media that rewards such content.