The OPs question is a good one. I understand if a car hits you. Some things are out of your control. What I am surprised by is that people here have said they hit cars or pedestrians. How is that possible? I routinely ride at 20-30mph and have had many pedestrians walk out in front of me, cyclists run red lights in front of me, car doors open, and cars pull out of driveways. I have never hit any of them.
I've had to jump off my bike a few times due to the lack of necessary distance to stop or slippery road conditions, but I've never hit anyone. If you maintain your brakes, have good reflexes and athletic skills, and pay attention to the road at all times (If I see one more cyclist on a cell phone I'm gonna' explode.), it doesn't seem reasonable that you should hit anyone, even at high speeds.
To those who have hit others, if your brakes were working properly, you have good reflexes and athletic skills, and you were completely focused on riding defensively, how did you hit something? What went wrong? I'm curious to know if there's something I'm overlooking. I'd like to keep my accident-free streak going.