In "The Young Life Of Frederick Douglass" why didn't Douglass initially realize he was a slave

The mistress’s initial kindness had a greater effect because it was during that time that she taught Douglass to read, an event which had enormous impact on his life. He acknowledges this when he says, “Mistress, in teaching me the alphabet, had given me the inch, and no precaution could prevent me from taking the ell.”  People are fed and sustained not only by food, but also by ideas and understanding.  Douglass finds vindication for his belief that slavery is wrong. Douglass “was led to abhor and detest” his enslavers. Douglass comes to feel that learning to read had been a curse rather than a blessing.  

    He thinks that if he were an animal, he wouldn’t have the ability to think and worry about his circumstances. Now that he can read, Douglass is tormented by his constant thoughts about his life as a slave and the impossibility of freedom. He regards slaveholders as “a band of successful robbers” and as “the meanest as well as the most wicked of men. Douglass’s purpose is to express his thoughts and feelings about being enslaved and about the effects of literacy. He relates three events that help him achieve his goal: his mistress teaching him to read, his further pursuit of instruction from “all the little white boys,” and the acquisition of certain reading materials that encouraged his own thoughts and feelings about slavery.

i believe it’s the first one, but it could be the second! not the third or fourth.

explanation: