Every deep thinker is more afraid of being understood than of being misunderstood.
Every person that has a thought that they want to share, is always subconsciously thinking of what people's reaction to it will be. The highly decorated thinkers of our time will go a step further even, and will be nervous if people will understand it at all or if it will go right over their heads and won't even pay attention to it. What Nietzsche is trying to say is that people are always self-conscious about their thoughts, but many aren't trying to sound extremely smart, rather they are trying to inform the people and share their knowledge.