Answer:
The self-perception theory.
Step-by-step explanation:
The SPT explains how people people develop and explain their new attitudes by observing their own behaviour and determining what caused it or what happened. Like in the example: Alex had never gone to the gym before but, after going several times, she concluded it was important to her. She interpreted her attitude as she might interpret others behaviors, she compared herself before and after going to the gym and determined it was important.