> how I feel does affect what I decide to do (or not do) next.
Not being affected by your feeling is a skill, that you can train. First you need to start noticing when you are in a state that affects your decisions poorly. This requires some free time thinking and reflecting on how you behaved in such situation after the dust settles. Then you can start trying to calm yourself in such situations. You need to override your impulses and that needs to be trained, you may not succeed first several times, but please keep trying.
With an extremely important caveat. Learning how to control impulses in the heat of the moment is important, but they need to be unpacked and properly processed as soon as possible.
If you do this poorly you can train yourself to be a stone cold robot who doesn't appear to react to anything emotionally. You might think you've succeeded but all you've done is lose touch with your own emotions.
I think it is also possible to just acknowledge the emotions in the heat of the moment, "process" them quickly as unproductive for the situation, and let them go their way.
Like the grandparent comment, I agree that this naturally requires training and effort. I also find that to be a more constructive way than to "suppress" your impulses/emotions for an unpacking later. Not saying you were necessarily directly advocating for that, just something that your comment made me think.
I think you and the person you are responding to are both correct. He added some important details and you added smaller but important details. Reality has a lot of nuances and different situations call for slightly different rules.
Meditation is also extremely useful for this. In breath-based meditation, you focus your mind on your breathing and try to eliminate thoughts. Obviously your mind gets bored and you begin to think of other things. Once you recognize that you're losing focus, you simply return to your breath. Over and over. Over time, you gain the ability to view your thoughts and emotions as easily disposable. It takes time but you can actually recognize that you're being affected by emotion, able to let go of thoughts, and be more present in the moment.
It's not hard; you just have to commit to it :)