The afterword seems kind of weak as it tries to return to the question of what quantum mechanics "means" and then... sort of doesn't really do that. It goes on to describe an "ethereal" influence distinct from causal influence, which is to say an "influence" that doesn't actually do anything at all. That's pretty disappointing.
The simplest explanation of what measurement actually is, in a quantum sense, is that it's the act of entangling your brain with whatever amplitude configuration represents the experiment we're interested in looking at. Basically the amplitude goes from looking like "brain * (result A + result B)" to "brain A * result A + brain B * result B". Brain A at that point can't communicate in any meaningful way with brain B because there isn't any causal relationship between the two anymore, so in a sense the brain has "split" and this is what we call decoherence. But for brain A to suppose that brain B has vanished in a puff of smoke, that is to say to privilege brain A over brain B, needlessly complicates the theory. It is the same as saying that since you can't see a thing anymore, it must not exist, and trying to build an entire physics based around what happens after you close your eyes.
The simplest explanation of what measurement actually is, in a quantum sense, is that it's the act of entangling your brain with whatever amplitude configuration represents the experiment we're interested in looking at. Basically the amplitude goes from looking like "brain * (result A + result B)" to "brain A * result A + brain B * result B". Brain A at that point can't communicate in any meaningful way with brain B because there isn't any causal relationship between the two anymore, so in a sense the brain has "split" and this is what we call decoherence. But for brain A to suppose that brain B has vanished in a puff of smoke, that is to say to privilege brain A over brain B, needlessly complicates the theory. It is the same as saying that since you can't see a thing anymore, it must not exist, and trying to build an entire physics based around what happens after you close your eyes.