"Why," you may ask, "do I need a theme song?" Well, you don't need a theme song but it might be a good idea.
Hear me out (pun intended).
Humans by nature are very empathetic beings and our mood is often affected by our environment. How we feel can be influenced by what our five senses tell us about our surroundings -- sound in particular has effect on us in the form of the music that we listen to. For example, a recent scientific study claimed that participants who listened to sad music judged a neutral set of images in a more negative way than participants who viewed the same images after listening to more upbeat music. (http://www.sciencedirect.com/science/article/pii/S0304394009003279)
What does this mean? Well, the music and environment that we choose to surround ourselves with has a great impact on how we perceive the world around us and how we perceive ourselves as well. Having your own personal theme song could actually affect how you deal with the world around you. Imagine starting your day listening to the Superman theme song or Survivor's "Eye of the Tiger" on your way to work... you might walk with a spring in your step and feel like you could take on the world. You'd feel pretty pumped wouldn't you? And that's not a bad thing.
And that's why I think it's important for you to have a personal theme song -- listening to something positive might help psych you up the next time you're headed to another meeting at the office, or before you're about to make that presentation to the rest of the team. It'll make you feel like the hero of your own personal movie, or the champion fighter about to head into battle. Or if you're Ricky Vaughn, get the Cleveland Indians into the Playoffs.