One Day

My interpretation is a lot like what @SC7 said. I also think the song is about being shy and struggling with being confident and trying to force yourself to be more confident but it's not that simple. I used to be very shy and quiet in high school, I still am a little shy but I have improved and become more confident. When he says,

                     "As your heart gets bigger
                      And you try to figure out
                      What's it all about?"

This means that every day you're trying to become a better and kinder person because you care about others and you want to be acknowledged and accepted by others. Even this is who you are, you struggling with accepting and loving yourself because you think everyone else hasn't accepted you yet. Which also correlates with "To shy to say that you need help. You and everybody else."

                     "As your skin gets thicker
                      And you try to figure out
                      What's all about."

To have "thick skin" means to be able to take criticism from others without taking offense or without caring about what they say. Yet, at the same time you're trying to figure out how to be accepted by others. People like this usually are very humble. Which also correlates with the line "to shy to say that you need help." Given that, humble people don't speak up about they're needs or desires because they don't entitle themselves or put themselves above others. Humble people have big hearts, thick skin and can be shy and they constantly spend time worrying about themselves and the people around them.

Basically, the song is about being the "shy guy" and constantly striving to become a better person every day. However, you need to stop worrying and be yourself because the problem isn't being accepted by others; the problem is that you have not accepted yourself yet and your wasting your time worrying about it. You should still strive to become a better person, but don't be too hard on yourself. People do accept you, but they won't come to you first most of the time. Don't waste away your life hiding from others. Show them who you truly are. You can't force yourself to become confident and fake it. You have to accept and love yourself for who you are and then your confidence will come naturally. People will notice it and they'll gravitate towards you. This was my personal experience. Appreciate life and the people around you because one day all of it will be gone. That is what I believe One Day is about.