There are people who act like thermostats who change the temperature of a room, introducing new ideas and making things happen. There are people who are thermometers who notice changes in temperature in the room, quickly reacting to their surroundings. And lastly, there are bystanders who need to be told what's happening around them. While people change between them based on their surroundings, on the whole behave one way more than others. Which type of person do you strive to be?
Some people can change the mood of a room simply by walking in. Often before they say anything, we're able to gauge what role they're likely to play. While at first this may seem like another way of describing leaders and followers, it's important to note that leaders need both approaches (they shouldn't be bystanders) to effectively introduce change.