I thought knowledge was enough for liberation, but Chapter 50 mentions even a wise person can have problems. Why is a Guru so essential?

Chapter 50 explains that while knowledge leads to liberation, it can be corrupted by doubt ('vikalpa'). It states that ignorance manifests from doubt and cannot be removed without a Guru. Even a supreme knower like Shuka is said to have suffered a loss due to doubt. When doubt enters knowledge, a wise person can become prideful. The text uses an analogy, stating that a single drop of fermented gruel ruins a large pot of milk. Therefore, a Guru is essential to help remove this foundational ignorance, purify the mind, and allow infinite, true knowledge to manifest.