This is clearly irrational. Chocolate cake is way better ...

(otherwise good point)

We’d like to see you make a rational, purely logic-based, and objective line of argumentation to justify why you like lemon cake instead of chocolate cake.

A shot at the why, would be that his digestion system might handle lemon better than chocolate, in combination with aquired taste, like the good memory of eating the first lemon cake at his birthday party and so on.

But objectivly proofing it, would require a very complex bio-chemical anaylsis of his digestion and neurological system as well as a deep psychoanalysis. Interesting research probably, but not necessary for determining that objectivly lemon cake has a higher value to him, because he simply likes it more.

Not sure why you're being so demanding?

Acting against what makes you feel better is rational. I don't think that's controversial.

maybe his nervous system randomly prefer it?

If you're Betty Crocker and only 10% of your customers want lemon cake mix but 80% want and buy chocolate...yes, it does cost more to make lemon cake mix, because you buy chocolate ingredients at nine times the volume you do lemon.

If you're a cake mix company that only sells chocolate cake mix, switching up production to include vanilla has expenses all by itself. You now have to manage extra ingredients in your supply chain, schedule time to switch production and all the overhead and downtime in doing so...and your factory-to-retail logistics chain is now both more complicated and split between the two products.

If you retail cake mixes, why would you dedicate capital, storage, and shelf space to something that sells at one ninth the rate?

Etc.

I don’t understand this comment - the premise was the two items cost the same to make.

Given that premise, it’s still possible to value one less than the other.

Given another premise that wasn’t in the comment… we’ll you can still value one less than the other but so what?

I don't see how not liking chocolate could be by any stretch of the imagination "rational".

You can swap it out for any other preference - that's not the important bit.

In continued good-spirited-conversation - if you get sick every time you eat something containing chocolate, I think it's completely rational to form an aversion to it.

I get pimples!