1) Geometry analysis. The program has to analyze the geometry in the room, deciding what areas are passable and what the sensible routes are. This can get to be really complicated. Remember that AI doesn’t understand “furniture” vs. “hallways”. It’s all just “shapes” to the AI. It sees the shortest-distance path across the room requires it to go up a step, then down a step. Except, that “step” is actually a footlocker, and people usually walk around those. Humans can skip the two-step flight of stairs and hop up onto a deck or porch, but we usually take the stairs. On the other hand, we’ll hop over a low fence or wall on the edge of a field rather than go around. But I won’t jump over a similar-sized “wall” if it’s actually the countertop island in the middle of the kitchen, or the dining room table. If I walk around the yard, I walk on the level parts, and avoid the awkward feeling of traveling horizontally across the face of a hill. I’ll generally avoid walking in paces where I have to duck, and I walk around desks rather than crawl under them. It becomes very hard to make the AI choose the right thing without a few hints from the level designer about whether this bit of geometry is a thing to be walked around, through, climbed over, or avoided.