In Quantum Mechanics, it has been observed that certain particles that have two options (i.e. going left or going right) actually do both at the same time when we're not looking at them and only make their final "choice" (left or right) when we observe them. That's downright weird if not magical. From what I've read elsewhere, both probabilities occur. We go along with one of them (i.e. it goes left) while a parallel universe spins off based on the other probability (where it went right).
The whelkies would simply carry a property that affects the probability field around objects and events in favor of the bearer, moreso with those who were the most in tune with it (i.e. whom it was meant for).
No, but really. Leave it to Quantum Mechanics to offer an explanation to the question ! If the Whelkie could behave as a quantum particle, it in theory would follow all avenues in search of the right person when we are not paying attention and at the moment one is looking it will decide to follow the path that was successful and led to the place it needs to be. Problem solved ! Never at the wrong person

Schrodinger's cat indeed !