Ulysses S. Grant, the 18th President of the United States, was nicknamed "Unconditional Surrender" Grant during the US Civil War. He earned this dubious title for his willingness to fight a battle until victory was earned, regardless of the loss of human life on either side. With this in mind, I think it is safe to say that, had he had the opportunity to play it, he probably still would have been pushed to the brink by the war of attrition that is Ninja Gaiden.
Modern gamers and classic gamers no doubt are already aware of the aura of impossibility that surrounds the Tecmo saga, which has been well documented in recent years with the revival of the series. It is not for the meek of heart or the impatient of mind. In fact, even these folks have likely thrown a control or two while playing one of the titles in the franchise. To best exemplify the difficulty that is, take a look at this animation, which gets right to the painful point:
It is this very difficulty that has relegated Ninja Gaiden to the Backlog for so long. It's a fun game. It's a game that has gotten a lot of play by me. It just also happens to be a game that 1.) Doesn't have any means of saving nor stage select, and 2.) is infuriatingly tough to play through to the end in one sitting (that is, if you can get to the end). I have spent hours upon hours upon hours throughout my life revisiting the original game, playing through the levels I have played so many times before, and still getting my ass royally kicked. It was only recently that I reached the end of the game, only to come to the abrupt realization that I was not going to be able to beat the final boss without losing my mind, playing the game for days on end, or both. I passed on the opportunity; I haven't regretted it. Maybe one day, I will find the time and the willpower (and the self-loathing) necessary to vanquish that beast once and for all. Until then, it is an accepted member of the Backlog for obvious reasons.