According to the author, why is it important to maintain an open mind?

Lisa Randall's book underscores the necessity of maintaining an open mind in theoretical physics—as in many other areas of intellectual pursuit. Surely there was more than the king's gold that drove Christoper Columbus toward the Americas. If Columbus had a completely closed mind, he probably would never have taken his journey because of the danger of falling off the edge of the earth. If the Wright Brothers had truly believed that powered human flight was impossible, why would they have toiled to build their airplane? If the dark matter deniers hold onto their belief, they will undoubtedly be left behind in the forward march of astrophysics, as Randall's book makes clear.