The text mentions that even a great knower can suffer from doubt. What is the role of a Guru in overcoming this?

Chapter 50 explains that ignorance manifests from doubt, or 'vikalpa,' and that this cannot be removed without a Guru. It provides the powerful example of Shuka, a supreme knower who still suffered loss due to doubt. When doubt enters knowledge, it corrupts it, causing even a wise person to become prideful, much like a drop of fermented gruel ruins a whole pot of milk. The role of the Guru is therefore indispensable. A Guru is necessary to help a seeker first understand and then remove this fundamental ignorance. By removing doubt, the mind is purified, which allows infinite 'knowledge' to manifest and non-dual Samadhi to be attained.