Why am I so hard on myself?

This question plagues me. Constantly. Anyone who knows me well will tell you that I'm always hard on myself, for little or no reason at all, and it takes a lot more than a simple, "It's okay, " to reverse the damage.

Take today, for example. I went to use the restroom and - forgetting the exact location of my cell phone at that moment - dropped it into the toilet. Yes, it was in my back pocket. As I heard the splash and crash that comes with an electronic device plunging into toilet water (which was, thankfully, clean to this point), I thought all sorts of horrible things about myself. Now, several hours later as my phone still sits on my dresser flashing and refusing to either turn on or off, I'm still furious with myself. I've only had the thing a couple of months. Like a stubborn, spoiled child, I insisted on getting a Razor, and now what? I essentially flush it down the toilet. I was so mad at myself after it happened that I literally had to leave the house, go somewhere - anywhere - but here, just so that I wouldn't be in surroundings that would force me to think of my own clumsiness and idiocy and make me want to do something equally destructive to myself. Yes, I have those thoughts, and yes, sometimes there is something of a plan that develops in my mind as I dwell in self-loathing. That's why it was so important for me to get out of the house. When Scott comes home I'll have to tell him, and he won't be nearly as upset with me as I am, but I dread it all the same.....like a little kid who broke something incredibly valuable. Scott is not materialistic, nor is he even half as impatient with me as I am (and as I believe he should be), but he won't be thrilled at what I've done. I, on the other hand, have been punishing myself all afternoon by replaying those few seconds in my mind and thinking how amazingly stupid I must be to do something like that, and how irresponsible I must be, and how this and that and the other thing I must be. Why do I do this to myself? I wish I were different.