Once he entered the category of rage, he entered the category of error (Sifri, Matos 48).
The Talmud says that this passage refers to Moses, and that if it holds true of Moses, how much more so for people of lesser spirituality.
The difference between rage and anger is profound. While anger comes from an external stimulus (and therefore our feeling that it is beyond our control), rage comes from people permitting their anger to feed upon itself and intensify into fury.
Note that the above quote states that those who enter the "category" of rage have entered the "category" of error. In other words, even if they have not actually been violent in word or deed, but have lost their composure to the degree that they could lose control, they have thereby already entered the realm of error. Anything they say or do in such a state is likely to be wrong.
If we feel our anger is intensifying within ourselves, we should stop whatever we are doing. We will regret the harsh words and acts that we are likely to do. We should instead allow time to pass and then confide our feelings to a trusted friend, thus defusing the rage and allowing it to dissipate.