"The heart is indeed desperately wicked - who can know it?"
An example of how complex this is can be seen by examining the very nature of people passing from some level of darkness into some new level of light. Of course this is a "good" thing, however it actually feeds our yetzer haha in a subtle way, playing upon our innate desire to 'be right' which our egos cause us to assume as now "having the truth."
In addition to this being part of our nature, it is also made worse by western/Greek culture (versus the eastern/Oriental which Hebrew rests in). The western tends to see things as black/white, right/wrong, heaven/hell, etc. G-d and creation are far more complex than that.
This combination causes people to view themselves in terms of comparing "where they are now" to "where they came from." They believe they have gone from 'lies' to 'truth' in a definitive way.
This type of thinking strokes the ego, feeds the yetzer hara, causes a form of arrogance that cloaks itself in a false 'godliness', eliminates objectivity (as you are now 'led by G-d' you won't be wrong) and destroys possibilities of deeper learning and bringing tikkun to your soul and to the world. It's as authentic as Esau was.
Further, even those who manage to overcome the above, there then comes another subtle reality of 'understanding limitations on one's understanding' - regarding what we know. One can only go as far "in truth" or "knowing G-d" as we are capable of at any given moment. We may reach a level of understanding/truth that is as much as we are capable of.
This is a real challenge to the ego (even of a G-d loving person) as we can't resolve what seems to be a conflict between "turning to G-d" while still retaining some kind of "spiritual limitation." (i.e., "G-d would never hold us back regarding 'truth'.")
Much of this is due to the influence of Christian ideas that there is nothing we can do to improve ourselves before 'accepting Jesus' and after we do it's 'The Spirit" that does it. Incentive for improvement does not really exist.
In Torah-Judaism the idea is that one can 'max out' on what we're capable of at any given time. We can 'have 100 percent of the truth,' but it is only 100 percent of our current capability. We have pushed the envelope to the max but all this means is it is time to break through that envelope into a whole new one. We may (and likely will) have to reevaluate what "truth" was/is to us and that is not always so easy.
This doesn't jive with western/Greek/Christian thinking. It is "anathema" to it. (LOL)
This is where humility is taken to new levels. Humility is always the gate to the next path, and there lies the puzzle - the path of G-d has segments to is and the highest door always brings you entry to the lowest level of the next segment.
According to traditional understanding there are 42 segments to our journey. (A theoretical number) This aligns itself with the 42 segments of the journey of the Hebrews from Egypt to the land of Israel. It is expressed as the path of joining the bride to the groom.