How do social movements form their political strategies? The relevant theory pays considerable attention to structure, and argues that when political opportunities are open, movements are more likely to opt for a systemic political strategy; when they are closed, movements are expected to take a more revolutionary turn. However, political opportunities can make some options appear more ‘realistic’ and others less so, but movements don’t always behave ‘realistically’. They might explain when movements are more likely to mobilise and what repertoires they adopt once they do so, but they do not account for what happens earlier on: by what mechanisms the movements form their political strategies. Exploring the case of the cocaleros of the Chapare, this article argues that more emphasis should be placed on mechanisms that are internal to the movements, such as: (a) the resonance of other political experiences at home and abroad, (b) internal struggles for ideological hegemony, and (c) the political formation of their grassroots.