In 1859, Mark Twain became a riverboat pilot as he always dreamed of becoming. He saw how beautiful the river was as a whole, from the way it curved gracefully, how things were reflected on the surface, and the way the light would shine foreign colors on the water. As he became more experienced though, his perspective of the river changed and he saw just how dangerous the river could potentially be.
In the final paragraph from his essay, "Two Views of the Mississippi" he compares what he saw in the river to the way a doctor no longer sees the beauty in a woman's rosy cheeks. Since he has become more knowledgeable, does he automatically sees her cheeks as a possible disease? Just as the doctor saw the woman, Twain saw just how bad a simple log floating down the river, a tiny ripple in the water or even a low hanging branch could be. The beauty of the river was no longer what meets the eye. The tiny ripple in the water was something, living or inanimate, beneath the surface that could destroy his boat. The simple low hanging branch could get caught on his vessels steam stacks. Even the colors thrown onto the water could cause a distraction or glare, causing him to crash or go off course.
Throughout the entirety of "Two Views of the Mississippi", Mark is consistently asking the reader to think about whether it's worth having the knowledge if it meant the certain loss of caring for the all the beauty and wonderfulness that is in our world. He is wanting us to appreciate every little piece of beauty that this amazing world has to give us because once you start to learn of the dangers that they potentially could have.