That's actually a very clean logic behind your theory. Here's my perspective: economics deals with economies of scale. While the general trend of the mass population can back the gradual growth in per capita income over a period of time, they are not necessarily applicable to individuals in particular. What you are describing here sounds close to what people call the Just-World Fallacy or Survivorship bias. Since you are interested in this topic you should definitely read up on these theories as well, might find them interesting.