If I understand it correctly, a particle doesn't have a definite momentum and a definite position, but is in a superposition of multiple positions and momenta. And when we measure either of the two quantities, say, position, the wavefunction collapses to tell us where the particle is. Now when we measure the particle again, it will always be in that spot since we have changed its state. If that's true, then what exactly is the use of the uncertainty principle? If the measurement changes the state, wouldn't measurement of the other quantity be irrelevant? Or does the uncertainty principle tell us that the spread of the various positions of a particle is related to the spread of the various momenta that a particle can have?