Pick up litter is a good thing to do.
Jacob is taking a walk with his little sister Kate in the park eating a candy bar when he drops the wrapper.
Jacob wants to get rid of the candy wrapper.
Jacob stops to pick up the candy wrapper and disposes of it in a trash can.
Jacob simply ignores the wrapper and continues on his walk.
Kate sees this behavior and learns it is bad to leave trash around.
Kate sees this behavior as okay and begins to litter herself.