[imdoor]

Say there is a quantum system – a particle or something – that has an equal probability to collapse in either of two classical states if measured. Say there are two scientists in a laboratory who perform a measurement on that system. If your hypothesis is true, how do they agree on what they perceive when looking at the result of the measurement? Each brain would have to make an arbitrary decision on which of the two equally likely outcomes to perceive.

[FollowingTheDao]

How do all calculators know that 2+2=4?

But our mental system is not as perfect. Because a person with schizophrenia or someone on LSD they surely not see the same things we do.

[mistermann]

Well, consider some of the political disagreements we've had in the last decade or so, we have ample evidence that two different people can look at the exact same thing and arrive at opposite conclusions.