The quoted statement was referring to absolute socioeconomic status. I agree that relative movement is possible and I also know a lot of extremely hard-working

The quoted statement was referring to absolute socioeconomic status. I agree that relative movement is possible and I also know a lot of extremely hard-working people (both rich and poor) who have been successful and climbed a rung or two in their lives. My point was more that the average wealthy person I know doesn't seem to have a particularly greater or lesser "ability to do things" compared to the poor people I know. Whereas if the "ability to do things" was really a substantial socioeconomic equalizer then I would have expected that DO-ers would be over-represented the higher up the socioeconomic ladder you climb instead of evenly distributed at each level. Perhaps it's different at the very top and the very bottom? (As a contrast, in the military I found a positive correlation between an officer's rank and their ability to do things. Most of the colonels I worked with had an impressive intellect and drive, and even moreso with the generals I met.)