When I was 3 years old I remember my mother taking me to day-care for the first time in my life. I was scared and it was very hard for me to make friends. There I understood for first time the meaning of rather having one or two good friends than to have many of them and none of them really cherishing your friendship. That was an opinion I stuck to since and it pretty much had an effect on every one of my relationships.
Every single memory and experience has an impact on our lives and builds up our personalities. Sometimes more and sometimes less, but it is still very essential what kind of things has happened to us before. For example someone who has always been mocked about some quality he or she possesses, may become very sensitive about the matter later on. Or it may be something as serious as a Freudian theory about how our childhood affects our personality when we grow older. Whatever it is and no matter how aware are people about the impact of that issue on their lives, it most certainly will affect them somehow.
Why is then our past so important in development of our personalities? Well, maybe simply because the most of our thinking consists of remembering something we did couple of hours, two days or even many years ago. The more we think about something particular, the more it grows on us making the subject a part of who we are and controls what we do. The rest of the time we are dreaming or making plans for the future, and that is possible only of the construction of millions of different memories, schemes and expectations of the various outcomes.
That fact makes future a very flexible thing. If eventually our future is just a combination of our past, then we have some power to make it something we crave it to be. That is achievable by trying to live our lives in the best way for us as possible. That way everybody can become a person he or she wants to see themselves like.