According to Sarny, why is it bad for a slave to run away?

According to Sarny, it's bad for a slave to run away because "nobody ever gets away."

What Sarny means is that she's never known a slave to succeed in escaping. Sarny doesn't believe it's wrong for a slave to run away; she merely thinks that running away isn't a worthwhile enterprise, because there's so little chance for success.

In the book, she cites three examples of slaves who tried to flee. One was an old slave named Jim. Waller, the plantation owner, had set his ferocious dogs on Jim once he heard about the slave's escape. Jim had run as far as he could, but he had to eventually climb a tree to get away from the baying dogs. However, the tree he climbed was too close to the ground, and the hounds succeeded in tearing the bottom half of Jim's body to shreds. The old slave had died with his hands still holding on to the tree. Sarny tells us that Waller had ordered the slave's body to be left in its place for the carrion birds to feed on.

The second slave to run was a young man named Pawley. One night, Pawley was late in returning from a tryst with a girl from another plantation, and Waller set his dogs on Pawley when he found out. Even though Pawley was on his way home, the dogs were allowed to savage Pawley to within an inch of his life. After the vicious attack, Waller tied Pawley down and castrated him. However, the crude operation was a botched affair, and Pawley bled to death in his quarters.

Sarny also tells about Alice and how she tried to flee. Waller had set his dogs on Alice too and they tore the young woman to shreds. Alice had survived the brutal canine attack, but Mammy had to sew her up in her quarters. Sarny relates that Alice never made a sound during Mammy's ministrations.

So, Sarny says that it's bad for slaves to run away because there's so little chance for success. In her opinion, she doesn't think there's really any place to run to, although the rumors have reached her that slaves can flee north. Sarny reasons that since the North is too far away, there's no use hoping for an unattainable dream that will never be realized.