This study analyses the role of communication in social activism from models that surpass the mere emotional reaction, prior belief reinforcement or brand identification. This paper tests the hypothesis that a message focused on the cause (and its results) will motivate a previously sensitized audience depending on their interactions with source favorability. The methodology is based on the design of a bifactor experimental action result study 2 (failure versus success) x 2 valences (favorable versus unfavorable source) with the participation of 297 people who are pro-avoidance of evictions. The results allow us to infer that the messages from sources hostile to the cause that report negative results have the potential to emotionally and behaviorally motivate activists to a greater extent than messages with more positive results from favorable sources. The conclusions point to the dialogue between social injustice frames and pro-cause action emotions as a way to increase social mobilization. The theoretical and empirical implications of these findings are discussed in the present-day context of social media prevalence.