There are a lot of different things that can go wrong in a day, a week, a lifetime. As the famous quote by Charles R. Swindoll goes, "Life is 10% what happens to you and 90% how you react to it." This of course, is always more difficult than it sounds.
I think I learned to stay positive through a few different key teachers on my life. First, my parents were and are always positive and adaptable people, and I grew up thinking that was the only way to do it. Later in high school and college I had a lot of opportunities to travel abroad, and during those times in different cultures I learned a lot about broadening my view of the world (and therefore my problems seemed a little smaller). I also learned a lot about myself and grew a an even higher sense of self-reliance. As an adult, I have had a few select people in my career that served as the exact type of mentor I needed at a specific time to help me see the value of perseverance and staying positive. Someone really important once told me that he didn't think that I was dreaming big enough. Noted.
I have always worked very hard at everything that I do. I am hard wired that way, but really it is a life coping mechanism. If I work hard and I do my best, then I know I have done all that I can. If I stay positive, it is a sense of controlling what I can control by choosing my attitude. If I didn't do these things, and it didn't work out in my favor, I would always wonder if I could have changed the trajectory.
This methodology has always worked for me, and I refuse to accept defeat. I own the 90%, and I will not let it own me. When things get tough, take control of your 90%.