Why is this the answer?

The answer is halfway because this is a very clever riddle that makes you think carefully about the direction of the dog’s travel. When a dog, or anyone else, walks *into* a forest, they are moving from the very outside edge toward the center. Think of the forest like a giant, deep space. The blind dog starts on one side, which is the entrance, and every step it takes moves it farther *into* that large space of trees. The whole time the dog is traveling closer to the center of the trees, it is definitely walking *into* the forest. Now, we need to think about the exact moment when that journey officially changes. Imagine the forest is 10 miles wide from one edge to the other. When the dog has walked 5 miles, it is at the exact middle point, which is the *halfway* point. The riddle asks how far the dog will walk *into* the forest. The key to solving this word puzzle is realizing that once the dog has passed that exact center or halfway point, it is actually closer to the *other* side of the forest than the side it came from. This means that after the halfway mark, the dog is no longer moving *into* the forest, but is instead walking *out* of the forest toward the exit on the far side. The fact that the dog is blind does not matter at all, because the question is all about distance and the overall direction of the journey relative to the whole forest. A blind dog can walk as far as it wants, but it can only be considered walking *into* the forest until it reaches the point that is exactly in the middle. As soon as the dog takes one step past the halfway point, its path is leading it toward the final exit. So, it stops moving *into* the forest and starts moving *out* of it. This is why the dog can only walk *into* the forest until it gets to the halfway mark. It is a wonderful riddle for making sure you listen very closely to every single word.