OK, I'm not an expert on the endowment effect. But from what I recall, behavioral economists have found that if you randomly give a gift to half of a classroom, then offer everyone the option to sell their gift if they have one or buy one if they don't, very few transactions take place. This is considered odd because you'd expect naively that everyone values the gift according to a certain dollar amount before any gifting happens, and you'd expect to see lots of cases where people could gain by selling/buying a gift.

It sounds like maybe the way you're using the word "rational", anything that anyone does can be considered "rational" just by postulating the right utility function. I don't think that approximates the standard usage of the word.

If you prefer to place value on the fact of ownership, I recommend you avoid reading the GP, as it was directed at people who wanted to hack themselves to no longer place value on the fact of ownership. If you prefer not to, knowing that economists consider your impulses odd and not very useful (in a certain technical sense) might help.