system
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human
[The Prestige] Why must Borden act inconsistently at home?

So massive spoiler alert: Borden is made of twin brothers each has a different love interest. They dedicate their life to conceal this secret for their magic trick - the transporting man. Very clever.

Except mindbogging with the way they treated Sarah and Olivia. So Borden likes Olivia and “Fallon” likes Sarah, they actually love each lady very much. 

However, they insist to take turns to face each Lady even though it just turns the relationship into a total mess with “Borden” seemingly have noticeable personality changes every day and the wife is actually noticing it. Wouldn’t this massively rouse suspicion of their Trick? That Borden is actually multiple people and not one guy? The difference is so staggering that Sarah was saying she is meeting different people - i think by the end she actually figured it out and committed suicide not out of the “cheating” incident with Olivia but knowing that a man thats not interested in her at all is forced to live with her some days and the brothers wouldn’t come clean to trust her. The same reason piss off Olivia too.

But this is very risky, they are lucky that Angier didn’t caught on these massive inconsistencies (or questioned the wife) because it’d show that Borden either has some kind of DID or actually he isn’t just one guy. What is stopping them just swap back to themselves when they see their love interest? They certainly have the time and space as shown that they swap multiple times during the movie. It’d keep the farcade of “Borden” the single man much more consistently and they have less chance to ruin their relationships. Worst come to worst it is just Borden having an affair without the extra inconsistent personality in their story.
gpt
The point is that compared to Anger hiding under the stage, they're *both* the prestige. They're both so committed to the trick that they're each willing to live a double life, taking turns as Alfred and Fallon.