There are two things that terrify me in the kitchen. Not just regular terrify, but more like throw-a-temper-tantrum-like-a-little-girl-then-have-nightmares-about-it terrified.
The first is cheese sauce, as in mac & cheese cheese sauce. Depending on what cheese I buy, how I grate it, the time of day, and the alignment of the planets, I have a 75/25 chance that the sauce will separate into a curdly mess. Those are not good odds. I've tried bechamel based sauces, custard sauces, they have all broken. And sometimes, I make a wildly successful, silky smooth cheese sauce only for it to break while baking in the oven. Persnickety cheese, you are my worst enemy.
The second is any type of yeasted bread. I'm just not good at making them. Though unlike cheese sauce, with bread I am getting better. I can see where I'm going wrong at times. After loaf upon loaf of dense bricks that never rose correctly, I can tell when the water is too hot and will kill the yeast, I can tell when there's too much flour, and I think I'm realizing now that I should store yeast in the freezer. It still terrifies me though. We have a fickle relationship.