The Theory of Reason Action suggests people behave the way they do because that's how they intend to behave. And that they make their intentions up based on what their opinion or attitude is of social norms. If someone thinks the social norm of dressing up for a funeral or wedding is good, they will plan on or intend to dress up for a funeral or wedding. And if they intend to dress up for the wedding or funeral because they want to fit that social norm, that's likely what they will do. Their intention is a predictor of their behavior. Three things make up intention (or instrumentality): attitude or opinion of a behavior, how they subjectively view the norms, and if they feel like they have control over their behavior (maybe they don't own any dress clothes) (perception of their behavioral control). A combination of these factor influences if someone will act or behave a certain way in the Rationed Action Theory. They may disapprove of the norm of dressing up for weddings and funerals and not own dress clothes, and then will be less likely to intend on dressing up. Intention is kind of like motivation. There is also the factor or perceived power in the Reasoned Action Theory. Perceived power is the judgment of how hard or easy it will be to do something. For example, since I own dress clothes, it will be easy to dress up for a wedding or funeral. 

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Coleman MT, Pasternak RH. Effective strategies for behavior change. Prim Care. 2012 Jun;39(2):281-305. doi: 10.1016/j.pop.2012.03.004. PMID: 22608867.