My bad, I didn't say it very well. The point is, in de Broglie-Bohm theory, it is assumed that particles are material points that exist, have trajectories. The

My bad, I didn't say it very well. The point is, in de Broglie-Bohm theory, it is assumed that particles are material points that exist, have trajectories. The motion of the particles is influenced by \psi, kind of like motion of charged particle is influenced by electric field in EM theory. These particles and the \psi function are the subject of the theory, so they "really exist" in this theory. In Copenhagen theory, \psi is understood to be mere calculational device the main purpose of which is to get probabilities of results of measurements. There is no idea that particles actually are there moving along trajectories; the subject of the theory are results of measurements and \psi is only a theoretician's tool to get their possible values and probabilities.