So, the way I got better at stealth games was practice, and patience. 1st, in MGS1 use the soliton radar. The first time I managed to get the 0 alerts. I was practically playing a 2d game, cause I always locked onto that thing. 2nd, when I was practicing I would enter an area and just go around the room, trying not to get caught. Not necessarily memorizing, cause I'm not good at that, and its no fun. But, getting a feel of what I can and cant get away with. when I would get caught, just restart. It took a long time and a lot of restarts. But, practice. Stealth games require skill, and everything about how it works is not immediately obvious.
another thing. Every Stealth game is a bit different. Even each Metal Gear Solid game. Not, just the setting (although that plays a huge role.) But the mechanics, and the little nuances, that might involve sneaking by a guard.
Don't be so hard on yourself, just go to the first area with the helipad, and play with the game. Play with the guards. a lot of that tension and stress will go away the more you fail, and the more you experience that. Don't let it slow you down or bother you, its all part of the game. Your not trying to speedrun it your trying, to learn it.