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.
If you throw a pair of dice, do they still have to roll if their final positions are predetermined from the point that you let go?
One view is that even a deterministic mind still must execute. An illusion of the capacity to choose between multiple options might be necessary to considering those options which leads to the unavoidable conclusion.
