Timidity

Humans just tend to hold back. Why? Face it, it's because we're afraid.

Afraid of being wrong, afraid of not having the answers, afraid of losing something may it be a person or dignity.

Two quotes come to mind for this

"To dare is to lose one's footing momentarily.  To not dare is to lose oneself."  

"You'll always miss 100% of the shots you don't take."

Take a chance.
You may even surprise yourself.