This book has lots of actionable techniques on how to naturally increase the size and girth of your penis with no equipment. This might sound unpleasant, but it's a fact: We are living in a masculine world. We are living in a world that is idolizing masculine values - even our own language indirectly conveys this fact. Many words and expressions such as "man up" that mean "be strong/brave" assert (though indirectly) how the world views masculinity.
Among other issues such as general body physique, you'll find that most men actually care so much about improving sexual performance - they want to have longer sex and protect their masculine image in this respect, and if they think the penis size is the deterrent, it can lead to stress and anxiety if there is no available, working solution. I believe this is only a natural response to the expectations of the world we live in and the societal demands we cannot escape from.
Think about it; most women wouldn't want to give you any hope of having sex with you if they think you are not just gifted down there. If you have a small penis, perhaps showering with men around you will constantly remind you of how lacking you are in that area of your life, irrespective of how successful you are in other spheres of life. Obviously, your ego will be constantly bruised when the topic of penis sizes, sex, and related topics come up. And even when you go to urinals and other men who are gifted well don't shy from holding theirs with pride for anyone who cares to look to see it, you will constantly feel bad about yourself and how lacking you are. Your self-confidence and self-esteem takes a nosedive, which subsequently affects other aspects of your life.