In a quantum logic circuit, every "observation" can be thought of as ultimately compiling down into a controlled-Z gate between the qubit-you-want-to-measure A

In a quantum logic circuit, every "observation" can be thought of as ultimately compiling down into a controlled-Z gate between the qubit-you-want-to-measure A and a qubit-to-hold-the-measurement-result B. The interesting thing about the controlled-Z is that it is actually a symmetric operation. You could think of it as "if A is ON then apply a Z to B", but it is exactly equivalent to say it is performing an "if B is ON then apply a Z to A" effect. The truly symmetric description is "apply a -1 factor to the weight of cases where A and B are both ON". Because the controlled-Z is symmetric, and every measurement ultimately involves a controlled-Z, you can't move details about A into B without also kicking back details about B into A. When B is a big well-approximated-by-classical-physics system, the back-effect plays out in a way that we call collapse. Said another way, B (you and/or instruments) can't get information about A (the quantum system) without collapsing it.