The humans predict that Animal Farm will fail.
When Farmer Jones mistreats his animals and they rebel to the point that they kick the humans off the farm, the people are shocked at first, and then assume that the farm will not succeed.
At first, Jones brings a small army to try to take back the farm.
Jones and all his men, with half a dozen others from Foxwood and Pinchfield, had entered the five−barred gate and were coming up the cart−track that led to the farm. They were all carrying sticks, except Jones, who was marching ahead with a gun in his hands. Obviously they were going to attempt the recapture of the farm. (Ch. 4)
This is unsuccessful, because the animals are able to drive off the men. Jones assumed that he was going to be able to easily take back his farm from a group of dumb animals. That proved not the case.
While Jones whiles away his time in the bar drinking, the other farmers are concerned that same thing might happen on their farms.
Nevertheless, they were both thoroughly frightened by the rebellion on Animal Farm, and very anxious to prevent their own animals from learning too much about it. At first they pretended to laugh to scorn the idea of animals managing a farm for themselves. The whole thing would be over in a fortnight, they said. (Ch. 4)
The farmers, always opportunists, want to turn Jones’s misfortune into to their advantage. They know that the two farms next to Animal Farm are always on bad terms, and hope the whole thing will fall apart.
Animal Farm does attempt to make use of contact with local farms, for trading to get things that cannot be made on the farm. This is mostly due to the pigs’ greed, especially Napoleon's. This also seems to fail spectacularly.
All relations with Foxwood had been broken off; insulting messages had been sent to Pilkington. The pigeons had been told to avoid Pinchfield Farm and to alter their slogan from "Death to Frederick" to "Death to Pilkington." (Ch. 8)
The war between Frederick and Pilkington is another element Napoleon and his minions seek to use to his advantage. While most of the humans feel that Animal Farm will never succeed, these farmers know that there is little difference between the opportunistic, greedy pigs and the humans they replaced. By the end of the book, the animals watching the humans and the pigs can no longer tell the difference.
The lesson here is that you should never underestimate others. The humans underestimated the animals, and the animals underestimated the pigs. The end result was the pigs ending up in control of Animal Farm.