Invisible - not visible; not able to be perceived by the eye, concealed from sight; hidden
Barrier - anything serving to obstruct passage or to maintain separation, such as a fence or gate
"For most of us, there is an invisible barrier – an inner shield that keeps us from making the kind of impact we were meant to make in the world. Generally that shield is trying to protect us from something."
Mayo, Stacey. "Is There An Invisible Barrier Stopping You? | Balanced Living." Career Coaching, Career Counseling, Career Intuitive, Small Business Coach. 30 July 2009. Web. 28 Oct. 2010. <http://www.balancedliving.com/invisible-barrier-stopping/>.
"The phrase 'glass ceiling' refers to an invisible barrier that prevents someone from achieving further success... Instead of being able to achieve the same success, she is stopped by invisible forces that prevent her from rising further."
Napikoski , Linda. "Glass Ceiling for Women- The Invisible Barrier Known As the Glass Ceiling." Women's History - Comprehensive Women's History Research Guide. 19 June 2010. Web. 28 Oct. 2010.
"The most powerful forces of Nature are the invisible forces, so we find that the most powerful forces of man are his invisible forces, his spiritual force, and the only way in which the spiritual force can manifest is through the process of thinking. Thinking is the only activity which the spirit possesses, and thought is the only product of thinking."
Reninger, Elizabeth. ""The Master Key" by Charles Haanel." Taoism. Web. 28 Oct. 2010.http://taoism.about.com/od/themasterkey/a/MasterKey1.htm