Learning to share

What makes sharing and collaborating so hard for most people? I believe that most of us would agree that a group of minds will be stronger than any one single mind over time. What causes people to be unwilling to share their thoughts, opinions, and knowledge is fear. Fear of what? Fear of what others may think, of what others may say, of how others will respond, and/or of what others may do with what you share. At the end of the day isn't it always going to be better for the human race if something that we share or collaborate on helps make the world a better place for the next generation? Maybe its just me.