Which theory best explains why our actions can lead us to modify our attitudes?

Cognitive Dissonance Theory.

Explanation:

This theory was proposed by Leon Festinger and it centers on the idea that an individual tends to look for consistency within his/her cognition (beliefs, thoughts, opinions, ideas, etc.).

The dissonance occurs when the individual notices an inconsistency between his/her behaviors and thus has to change something in order for them to be compatible and consistent again.

In order for the consistency to appear again within the individual's attitudes, he/she might need to change his/her actions in order to do so.