The wave function in quantum mechanics does not predict what state of affairs will eventuate; it only specifies the probabilities. Any number of things might happen. Yet the observer taking measurements does not perceive an array of different states of affairs; he perceives just one state of affairs. Seemingly, the very act of observation does something to the system. But the wave function of the phenomenon the observer is measuring does not describe the act of measurement itself. So what is going on?
A number of solutions are suggested. Some physicists have proposed that reality is one thing, but the consciousness of the observer is, so to speak, something else. If the observer is merely human, then this sort of proposal is troubling for a lot of reasons. For if reality is what it is because I think it, then how did I myself come to be? And where does this leave you?
Surprisingly, Thomas Aquinas would have found such problems less disorienting than we do. We are thinking of just two things: Reality and human minds. But he is thinking of three: Physical reality, human minds, and the mind of God. The ideas in God's mind do not have the same relationship to things that the ideas in a human mind have.
In the case of a human being, things are the measure of mind. In other words, human concepts are not true in themselves; they are true only to the degree that they conform to how things are in reality. But in the case of the Creator, mind is the measure of things. That is, God's intellect really is true in itself; things are true only to the degree that they conform to His mind. (Summa Theologiae, I-II, Q. 93, Art. 1, ad 3.)