Whether it's that you're gay, bisexual, transgender, queer, or straight; whether it's that you're Mormon and you're worried about your co-workers finding out or that you're an atheist and you're worried about your co-workers finding out; whether it's that you actually love musicals or country music or ballet despite years of professing otherwise; whether it's that you secretly hate football or romantic comedies or fast & testimony meeting or your family's favorite board game in spite of social pressure to do otherwise; whether it's that you feel like you have a facade up when you act social and you're afraid people will find out that you're really not very outgoing at all but you can't change your public identity *now*!--WHATEVER it may be that you don't feel is sincere about yourself... come to grips with it today. Face it head on. It might be something that you want to embrace and tell other people about. Or it might be something that you want to work on improving but that you can't address until you accept that it's there. The first step is knowing yourself better and introducing more of your real self to the other people in your life.
Be honest with yourself. What are your flaws? What are your secret talents? Who do you have a secret crush on? (Married friends: disregard that last one) Let the appropriate people know. That might mean you just need to tell yourself, it might mean tell your best friend, it might mean tell your family, it might mean make it your facebook status in ALL CAPS, it might mean mailing it in to PostSecret. You know what's right for this secret for you right now.
And to bring this down from the wholly abstract and impersonal, I'll come out about an aspect of my personality I haven't really shared much of publicly: I'm really bad at sharing my inner thoughts and feelings with people. I always say I want a confidant, but I never take advantage of opportunities to have one. It would require actually confiding things.
So there's something for me to work on. How are you going to come out more fully today? For best results, it should be something you're scared to tell people. Do it anyways!