Jimin was a sweet person, gentle and naive, and maybe crossing the forest to visit his grandmother wasn't the best of the choices, but he did it anyways. He would be fine as long as he didn't leave the trail, as his mother had instructed,  but again, his mother hadn't told him there would be a big bad wolf lurking among the trees hunting him as if he was a small bunny. Jimin simply didn't know, he was a simple and naive boy, so how could he know?