What I get most frustrated about with myself is when I learn a lesson... and then remember I'd already learned that lesson not once, not twice, but a handful of times.
Never, I repeat never, hold a bunch of things in your hand, with one of them fragile enough to break if dropped, and then go about doing something without thinking about what may drop. I had the sugar bowl with lid and two narrow cans of tea in my hand as I tried to move some mugs around to reach a green tea whisk behind them. My hand tilted forward enough that the lid slid off and plummeted down to the hard tiled floor, resulting in a shattered mess. Why didn't I put it down first?