Usually it's because the song speaks directly to them, or of them, or something that they desire most.
I believe that if you strongly believe in your theme song and work hard for it, you will one day be singing it yourself proudly. :)
"Our deepest fear is not that we are inadequate. Our deepest fear is that we are powerful beyond measure. It is our light, not our darkness, that most frightens us. Your playing small does not serve the world. There is nothing enlightened about shrinking so that other people won't feel insecure around you. We are all meant to shine as children do. It's not just in some of us; it is in everyone. And as we let our own lights shine, we unconsciously give other people permission to do the same. As we are liberated from our own fear, our presence automatically liberates others."At the age of 20 you have been achieving numerous successes in life and have gained valuable experiences around the world. Let's continue to strive for greater heights in life for the Lord has great purpose for us here!
Your time is limited, so don’t waste it living someone else’s life. Don’t be trapped by dogma — which is living with the results of other people’s thinking. Don’t let the noise of others’ opinions drown out your own inner voice. And most important, have the courage to follow your heart and intuition. They somehow already know what you truly want to become. Everything else is secondary.To add from my end - Be strong. Be courageous. Persevere. Risk more than others thinks is safe. Dream more than others think is practical. Expect more than others think is possible. Be rebellious when it comes to something your heart truly madly deeply desire. I rejected a Shell scholarship because I wanted to study something that I can apply to me and my family's health, I ditched the idea of interning at an MNC because I prefer the hectic tasks in a start-up company, I declined an offer to work with an MNC once I left my 1st job because I know that's totally not what I want, I choose to do volunteery work in Korea once I graduate instead of finding a job because for my sake I'll be working anyway in the future, and many more, and that's how it made me who I am today. That's when I have more stories to tell.