Pulled out of the ditch

A guy drives into a ditch, but luckily, a farmer is there to help.

He hitches his horse, Buddy, up to the car and yells "Pull, Nellie, pull!"

Buddy doesn't move.

"Pull, Buster, pull!"

Buddy doesn't budge.

"Pull, Coco, pull!"

Nothing.

Then the farmer says "Pull, Buddy, pull!" and the horse drags the car out of the ditch.

Curious, the motorist asks the farmer why he kept calling his horse by the wrong name.

"Buddy's blind" said the farmer.

Spoiler:

"And if he thought he was the only one pulling, he wouldn't even try".