I want to dedicate this book to my parents, Vassilis and Nektarias, would like to thank for all their teachings, which helped me to have ethos, courage and emotions in my life. I would also like to dedicate this book to anyone who every time he stops at the traffic light he thinks he could make the world better, anyone who, when he sees a forest, can distinguish the sick tree and think he can treat it so the entire forest does not get sick. With all the above, we have something in common, thinking about a better world, developing but above all the same improvement, because in order to be able to improve those around you first you have to learn to improve yourself.