Each thing you add to your story is a drop of paint falling into clear water, it spreads through and colors everything.
Remember, when we're lost in a story, we're not passively reading about something that's happening to someone else.
Stories not only give us a much needed practice on figuring out what makes people tick, they give us insight into how we tick.
You cherry-pick events that are relevant to the story question and construct a gauntlet of challenge (read: the plot) that will force the protagonist to put his money where his mouth is. Think baptism by ever-escalating fire.
If I ask you to think about something, you can decide not to. But if I make you feel something? Now I have your attention.