If one follows this teaching, you will spend your entire life on introspection. "How am I doing? Is this acceptable to the Lord? Oh no, I should rather stop doing this and do more of such and such.".
That is not healthy to be overly introspective.
Which is why God went on to raise up Witness Lee to help us to learn to touch our human spirit - pray reading the word, calling on the Lord, and each holding to the Head Christ.
This the Lord went on to recover. Lee helped Christians to enter into many healthy teachings by teaching them to hold fast directly to the living Head , Christ in their spirit.
In this way the two men's ministries greatly complemented each other. It is the Lord's move of recovery and not man's.
Like fmf says, it drains the joy out of your spirit.
Then you follow the help you get from FMF. No one is stopping you to get help from wherever you think you receive it.
He has a thousand post out there criticizing, questioning, doubting, denying, dismissing the Christian gospel and experience. If you get more help living unto God from FMF then go get spiritual guidance from him.
I get more out of any paragraph of WN or WL frankly.
Not only that, it focuses on I, Me and Mine. Which inevitably leads to pride and superiority (if one succeeds) and depression and guilt if one doesn't.
The missionaries opposed Watchman Nee steadily. When he died as religious people often do, they whitewash the tombs of the prophets. They speak highly of them though while they lived they fought with them.
Certain Christians who was eager to promote Watchman Nee's messages after he died mostly promoted books on
individual spirituality. They did not present the balance of Nee's ministry which included fellowship, love, mutuality in the church life.
So as a result many people get a lopsided opinion that Watchman Nee's messages were all about introspection.
In the one sided exploitation of Nee's ministry to under appreciate his messages on the church and over stress his messages on individual spirituality, we see that this damaged some people's growth.