My Teacher taught that without a working with a Spiritual Teacher, progress past a certain point is basically not possible. The primary reason is that humility is one of the most important virtues a spiritual seeker must embody.
Humility in this case means humbly receiving the guidance of a Spiritual Teacher, someone who you trust as having a clean agenda, allows you to see what you cannot see. This very aspect causes untold anguish for many genuine seekers. This can be because of past conflicts with authority figures. One has to allow their Spiritual Teacher to become a trusted authority.
There are many challenges to moving deeper within to deeper spiritual experiences. One big issue is not asking someone further along the path to validate their spiritual experiences. This gives rise to people making up their own progress and slipping farther away from the Truth.
Is it hard to work with a Spiritual Teacher? Yes, it is very hard to allow someone to see you in your most vulnerable state. Working with a Spiritual Teacher generally begins with finding someone who consistently carries the consciousness of integrity and love. Attending an occasional lecture may not be enough for someone to trust that a Spiritual Teacher is the real deal.
You have to spend as much time as you need to observe the Teacher to be as certain as you can be that he or she has pure motives. One could argue that no one has 100% purity of intent. I would say that is true. However if you are going to set your bar so high as to only allow the Buddha, Jesus or Confucius to teach you, you won’t develop that humility that is needed. I encourage you to trust someone at some point.
True, no matter how far along a Teacher is, they are still human and have flaws. And true as well that it’s not that easy to find a real Spiritual Teacher that you resonate with and that is available in your geographical area. However, I firmly believe that if you are dead set in your intention to grow spiritually, you can find a Teacher to guide you.