Three possibilities come to mind:
Is there an evolutionary purpose?
Does it arise as a consequence of our mental activities, a sort of side effect of our thinking?
Is it given a priori (something we have to think in order to think at all)?
EDIT: Thanks for all the responses! Just one thing I saw come up a few times I’d like to address: a lot of people are asking ‘Why assume this?’ The answer is: it’s purely rhetorical! That said, I’m happy with a well thought-out ‘I dispute the premiss’ answer.
That’s unfortunate - you credited me with debating in good faith, yet won’t do the same.
You rather obviously knew that the way you attempted to frame my position was disparaging - if you hadn’t, you wouldn’t have felt the need to add that proviso to the end of your post. What you clearly attempted to do with that was to disparage the position, while asserting that you didn’t mean it personally.
Ah well.
I didn’t do what you said. Did you read the links?