Reason why what a person does is more important than what a person thinks

A famous quote, "Actions speak louder than words".
Imagine, thinking about feeding all of the hungry people in the world, it's a nice thought, right? But, it isn't an important thought because you're not able to do it, you cannot change the fact that people are starving; however, if you WERE able to feed every starving person instead of just thinking about it, that'd be important.

A person could say, "i'm going to get on a roller coaster today".

Let's suppose that they are afraid of roller coasters, and when they arrive at the amusement park, they don't get on, because they are afraid.

We can see here that actions would speak loader than words do, in this sense, this person thought that he was brave enough, but his actions said that he was not.