It's important to test your assumptions, and then learn from the feedback you get. In business this is critical. When it's paired with a passion it can be fun, and valuable experience. Right now I'm testing a new Amazon original paperback in Germany, France, Spain, Italy, and Japan and the Kindle version in Brazil, Mexico, and India via Facebook ads. Being a fan of human psychology, consumer behavior, and statistics (to a very limited degree!), this is fun for me. That shameless plug aside, it's important that we constantly ask ourselves why we think we're right about something, and test whenever possible.