> "Having the courage to go on when nobody believes in you"

If you're doing something that isn't like how people are used to things being done, is novel, or is contra to common beliefs, there's a good chance that nobody will believe in you. And in such situations, their lack of belief is not a reliable indicator of whether what you're doing is valid or correct. Most people's negative responses in such cases are emotional responses, not rational ones.

In such situations, "Being honest with themselves about whether what they are doing is actually working or not" and "Having the courage to go on when nobody believes in you" are not opposites.