After he escaped and fled to New England, he worked as a laborer in the shipbuilding industry. One of the things that struck him at the time was that slavery was a crippling institution in the South even for the slave owners. This was because he and the other laborers who toiled in these difficult jobs -- many of them former slaves like himself -- had a better standard of living than their slave masters in the South.
From de Tocqueville observing the difference between slave state Kentucky and free state Ohio:
“Upon the left bank of the stream the population is rare; from time to time one descries a troop of slaves loitering in the half-desert fields; the primaeval forest recurs at every turn; society seems to be asleep, man to be idle, and nature alone offers a scene of activity and of life. From the right bank, on the contrary, a confused hum is heard which proclaims the presence of industry; the fields are covered with abundant harvests, the elegance of the dwellings announces the taste and activity of the laborer, and man appears to be in the enjoyment of that wealth and contentment which is the reward of labor.”