For those of you who don't know, a textwall is when the entirety of the story is one paragraph. I don't mean it's one paragraph long, I mean that it's one thousand words and there's no second paragraph anywhere.

This is difficult to read because the wall of text, hence the name textwall, makes it near impossible to keep your place. You start thinking to yourself, "Did I read this sentence twice? Was this where I was? Did I skip a line?"

Even if you have the greatest plot in the history of the universe, many potential readers will be completely repelled by the idea of having to struggle through a textwall.

And now, a demonstration. I shall use some Warriors fanfic.

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Hawkheart stood, belly deep in blood stained snow. The three rogue cats stood in a half circle in front of him, baring their fangs and hissing, their eyes flashing with pleasure at seeing the great grey warrior bleed. Suddenly, one leapt at him, aiming for his throat, and Hawkheart jumped back enough to dodge. He threw himself forward in a last-ditch effort to take at least one more of these cats down with him. The pounce wasn't pretty, but it worked. His teeth sunk into the throat of the she-cat and he held her down with his claws, gagging on the scarlet tide that flooded down his throat and out the side of his jaws. "Thorn!" One of the rogues, a tom, threw himself on top of Hawkheart, pushing the tom down on the she-cat's now lifeless body. Coughing on the blood, trying to shake off the tom, Hawkheart rolled over and managed to get rid of the rogue before he could sink in his claws. "Give up," Hawkheart growled. "My Clan will never be bowed by the likes of you.""Shut up!" The tom threw himself forward again, the other cat joining in this time. Carried off his paws by the force of their blows, Hawkheart fought like a lion, claws flashing and teeth tearing, doing as much damage as he could before the light left him.

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A lot of words and no separation. It looks horrible, no one wants to look at that, especially when the dialogue is unparagraphed. It's just... Uhg. Disgusting.

So please, make sure you have appropriate spacing to make sure that your readers enjoy your story.