To understand the extent to which our actions affect others, try to change some of your most habitual behaviors.
Look at what happens when you look intently at your best friend, when you greet an exultant "hello" to a manager of your company who is usually taciturn, or leave your things in the next seat during rush hour in the subway. And then try to act differently: hold the door for a stranger, send a message to a friend who is having trouble in their relationship, help your mother.
Pay attention to how all these changes affect you and the people around you.