This is a theory about what shapes our behavior.
The theory says that what drives our behavior are our intentions. And that what shapes our intentions are our attitudes towards the behavior, our perceived control over the particular behavior, and social norms about the behavior. Do other people think it is a good behavior? That will lead to good things?
Let's get practical. I always go to bed too late. To change my behavior and go to bed earlier, I need to want to go to bed earlier. And this is shaped by whether I think going to bed earlier is a good thing. What are the subjective norms around bed time and wake-up time? And do I feel like I am in control of going to bed earlier? Do I feel capable?
We like to use the Theory of Reasoned Action to help us generate ideas about potential levers of behavior change. How could we help people feel more capable, and more in control? Could we build people's skills? Could we give people feedback? Could we help people to practice new behaviors in-context? And how could we influence subjective norms? Could we change people's reference points? Peer groups? The messages they receive in their environment?
And herein lies some of the limitations of the Theory of Reasoned Action. Which focuses very much on the individual. On their beliefs and perceived control. Rather than on the environment around them.
That's why we tend to draw on a number of different behavior change theories. Including Urie Bronfenbrenner's Ecological Systems Theory. All as prompts & inspiration for idea generation & prototyping.