Two opposite mistakes

The first mistake says anger is always from Shaytan, so if you are angry you have let him in. That takes a normal human state, one that prophets are described as having, and turns it into evidence of a spiritual fault. It adds shame to a situation in which shame is already one of the drivers.

The second mistake goes the other way. It says anger is honesty, that holding it in is fake, and that whatever comes out in the heat of it is the truth finally arriving.

The tradition does not say either of these. It treats anger as a faculty, something that has a proper use and that goes wrong by excess and also by being absent altogether. What is being trained is not the feeling. It is what the feeling is allowed to do.