I can hardly name a single kind of person who thinks "You know what? I don't want things to be fair, so i'm going to try to take as much stuff as I can if this bitch is to break up with me >:D"
Eh, to expand on what Brovo said humans are emotional creatures by nature.
People usually look through things with a personal and bias lens, not a objective and critical lens.
And this is especially true in Relationships, which is essentially just emotions towards one another.
And even Logical People can fall for this trap very easily in their relationship, may it out of blind love, fear to hurt them, guilt etc.
For a personal example I generally find myself fairly capable of taking a step back, absorbing the facts and then working on a conclusion.
However, Relationships (as far as past experience goes for me, last case being over 2 years ago) is an entirely different ball game.
Suddenly there's this individual who I care about, my feelings for them grow strong, I care about their well being and our personal bond completely.
And as a result I'll lose a lot of sense of judgement, doing rather brash/illogical things, become more clingy, protective etc.
And in this topic of Prenups more specifically.
I'm completely ok with such a contract... now.
But go back a few years ago? I was
way into the "Love will get us through. We should trust each other blindly" mentality.
(Granted I was a Teenager at the time) where even any sort of logical precaution fired off paranoia in my head along the lines of "Does she not trust me? What did I do wrong? Why doesn't she love me?" etc.
And in all honesty, if I hadn't had friends in high school with such a good on their shoulders to help me out back then I'm not sure if I would have been able to kick that sort of mentality (or at least control it) today.