Repeating the same measurement results in the same answers.
Let’s consider the Stern–Gerlach experiment, and try to measure the spin of an electron in the vertical direction. If we pass, let’s say, 5 electrons through it, and the first vertical measurement returns the sequence SNSSN, where S represents South and N represents North, then no matter how many times we stack the apparatus behind one another and take the vertical measurement, they all would result in the same sequence, i.e. SNSSN.