Ross was a firm believer that you could not force circumstance. You could buckle your seat belt, but still crash the car. You could throw yourself in front of an oncoming train, but somehow survive. You could wait for years to find a ghost, and then have one sneak up on you when you were too busy falling in love with a woman to pay attention. To that end, he made the conscious decision to stop waiting for Lia. When he least expected her, that was when she would show up.