Define 'Normal'

I tend to find that with mos games, the very first choice you have to make is often the hardest one, but at the same time it doesn't apply to all games. The choice I'm talking about is of course the difficulty level. I try to make sure that when I start a game, I play through it on the standard difficulty level, but the issue is, when you come into a new game, how do you know how hard its going to be? What is considered 'Standard' difficulty for one game might be the equivalent of 'hard' on another. I suppose the easy solution is to play it and see, but where's the fun in that?
Probably the most famous set of difficulty levels aside from those of Halo and CoD. they're from DOOM if you weren't aware, but tell me here, is Hurt Me Plenty like Normal, or Hard mode?
See it's also not a good idea to this because of difficulty curves, I'm thinking more about fighting games here but it applies to most games, if a game doesn't give you some easy levels to begin with, it's worried you'll lose interest through your frustration at being unable to complete the first stage.
with an average 2D fighter like blazblue, for example, you'll start arcade mode against a character that barely attacks or guards and just jumps around every now and then, an easy win and possibly a reason to up the difficulty a bit, right? WRONG.
Even 'Standard' difficulty opponents can pull off shit like like this in the later stages.
By the time you reach stage 6 or so, you're getting near the end and the difficulty's notched way up. You come against an opponent that's quick, can land seemingly insane combos, knows exactly how to break your guard and seemingly never gives a chance to counter. You can land a bit of damage, but you can never quite take them down to 0, or if you can, rarely twice for a 2-0 or 2-1 victory. I see myself as average when it comes to fighters, i.e. I know a few combos and all the basics, plus the button combinations for the super powerful full SP bar super moves, but that's about it, if push comes to shove I just randomly hit buttons and wiggle the analogue stick in the hope I accidentally land a full combo. Yeah, it never happens.
Probably the ideal difficulty screen you could see, both thanks to the great description of what the difficulty means and of course the insult to Justin Bieber
The point is, it's very frustrating and a good game has a good balance between far too easy and nye-on impossible hard for the 'average' gamer, the only problem that comes with this, is that how do we know how good the 'average' gamer is? That's a question for another day.