Years ago I've a friend who went into study of the art of the ninja and within 6 months he gotten his black belt. He also gotten the full uniform, swords, stars, claw gloves and other stuff that he shouldn't be telling me about, but because I was such a trusted friend...
We went out on his night stealth training, him disappearing into the woods and I giving him time enough for me to smoke a cigarette (100's even) and then go looking for him. After the agreed hour had passed I went on back to the truck to wait. He showed up a minute later. According to him, he was close enough to touch me a number of times and had even walked behind me for a good 50 feet before I turned around (of course not seeing him there)... doesn't mean I didn't hear him, :wink2: Being pitch black (moonless) night and denied a light for myself ... yeah of course someone dressed all in black would be able to hide without much difficulty in the shadows of a deep dark blackened wooded area.
Being stealthy isn't that difficult. Elite military forces and snipers are trained to do the same thing... and in broad day-light no less for some missions. In my much younger days I had a very brief career as a thief, which also required some stealthy movements and "blending" into the shadows as it were... I was able to pull it off without any training, just common sense.
Hollywood has definitely magnified the Ninja legend. It's sad really.