Let's take a logical approach to it.
Anybody who has a product preference usually has a thought out chain of reasoning that compares the percieved benefits and advantages of their choice to the alternative. There aren't too many people adamantly shouting "Apple Rules!" who don't have a list they can rattle off of why they think it is so.
If you listen to that person, it all makes sense and is very logical and isn't an emotional decision to them. Even if we know they're totally wrong and being emotional about it.
I suspect that a mental groove gets worn into the brain about the topic, that as one internally contemplates the reasons for the decision, it adds an emotional weight to it.
Another interesting effect going on in the brain, is that the emotional part of the brain fires off to make a decision before the rationalizing part. People quite literally make a choice willy-nilly and then their brain rationalizes why that choice makes sense.
This effect is probably reinforced by my first concept, that the more you reflect on your decision and justify it to yourself, the more you reinforce the emotional response.
Couple all this with the way people tend to talk about decisions, it almost always tends to trigger a defensive justification response, rather than a calm "let me self-audit that decision and determine if that was a choice worth repeating"
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