Most highly-successful people were fired from established companies early in their careers. Many others resigned from companies in their field of choice, typically out of frustration because the company moved too slowly, was too antagonistic towards their ideas, or simply bored them. It's a common experience since most existing companies are set up to optimize what has already been created. Few have the capacity to once again disrupt their own creation. Often, you must be the one who creates an entirely new creation.