Their far selves will most likely have the same basic disposition, even if different circumstances. I think that's the point being made here: that people neglect to think of how they react to events, emotionally (eg. how happy they get when happy things happen) and only think of the events themselves. A future accountant may be happier than a future actor, but neither of them would guess it.
The scientists who conducted this interesting study...
found that our natural sunny or negative dispositions might be a more powerful predictor of future happiness than any specific event. They also discovered that most of us ignore our own personalities when we think about what lies ahead -- and thus miscalculate our future feelings.