( CNN ) -- Dear Girls of the World , . I did n't start playing soccer imagining I would be scoring goals in the Olympics or representing my country at the World Cup . I started playing soccer , and sports in general , as a way to simply make friends . On the field , I was able to hang out with kids my age , kick the ball around and just have a good time . What I did n't realize at the time was that soccer would do more for me than I could ever imagine . At a young age , soccer taught me about leadership and sportsmanship and what it means to be a good teammate . Most importantly , it taught me the power of confidence . Confidence is not something that is always easy to find . Often , being the new girl on a team or being in a group breeds insecurities . I have joined countless teams where I was the new girl , and I was never immune to those feelings of self-doubt . I have learned that by pushing aside those insecurities and rediscovering my inner confidence , I become a better teammate and person . That 's why I wrote the book series , `` The Kicks , '' to show girls the importance of maintaining confidence when faced with new ( and sometimes scary ! ) opportunities . While the book is aimed at middle schoolers , the lessons in it are ones that I think hold true across all ages . Joining the U.S. Women 's National Soccer Team was intimidating to say the least . I joined a team with women who I had looked up to for years , and at just 20 , how was I supposed to fit in with them ? I was nervous and overwhelmed . But I knew that I was capable of competing with them so I pushed myself outside of my comfort zone in order to be the best player I could be . I now call these girls more than just my friends . They are my sisters , and together we support each other through thick and thin . I 'm so grateful to have some amazing women around me to help me learn and grow . Confidence has carried me on and off the pitch , through high school in California , college at UC Berkeley and now professionally for the U.S. Women 's National Team and the Portland Thorns . I have had to adjust to new surroundings , meet new people and have been challenged by different situations . All of those experiences , while nerve-wracking at the time , have empowered me to grow stronger . It 's important that as women , we stand up for ourselves , stand up for our peers and show the power that confidence can have for women everywhere . -- Alex Morgan . Read more open letters . Open letter from Christiane Amanpour : It 's time to power the world . Open letter from Queen Rania of Jordan : More than tiaras and cupcakes . More : CNN 's `` Girl Rising '' How to help | Take action with 10x10 .
Alex Morgan writes an open letter to girls of the world .