"To be great is to be misunderstood." This quote means that it's okay to change your mind. You can have a different opinion everyday. It's your mind and you can think whatever you want to. .
There are many great people in history who were considered misunderstood. Thomas Alva Edison was a man who locked himself away to spend time conducting scientific experiments. He excelled in the ability to bring together seemingly unrelated scientific principles. Because of this, he was able to invent and discover things others may have missed. He was a very misunderstood man, but because of that, he came to be known as having one of the greatest minds ever.
Some people were so misunderstood in their time that they were persecuted because of their thoughts and beliefs. Socrates, a Greek philosopher, spent his life seeking knowledge of what was right, in means of finding a universal truth. Professing to be completely ignorant himself, he would converse with people of power in Athens, asking questions that led them to contradict themselves and become confused. This made them furious and Socrates made enemies of many powerful people in Athens. This ultimately led to his trial and execution. Regardless, he is still known to be one of the greatest philosophers of all time.
This is why the need to express your own opinion and beliefs is so important. For anyone to achieve greatness they have to believe in themselves and be strong enough to follow their own way of thinking, even when others don't understand and ridicule them.