Why does Chapter 50 say a Guru is so important for overcoming doubt?

Chapter 50 emphasizes that a Guru is indispensable because ignorance often manifests from doubt, or 'vikalpa,' which cannot be removed without a Guru's guidance. The text illustrates this by pointing out that even a supreme knower like Shuka suffered a loss due to doubt. It uses a powerful analogy, stating that just as a single drop of fermented gruel can spoil a large pot of milk, doubt can enter knowledge and corrupt it, making even a wise person prideful. Therefore, the Guru's role is to help remove this doubt, purify the mind, and allow infinite, true knowledge to manifest, leading to non-dual Samadhi.