Keep in mind that one failure can cause a cascading effect. If one breaks, the tipping can and often will cause others to fail. Sudden wind gusts will push cars off stands too.
My experience: (warning! Quite graphic. I used to have pictures of my injuries but lost them when the website went down suddenly)
Another thing no-one seems to account for is ground movement. Be it soft ground or a Geo movement (earthquake). I was the near fatal victim of the latter. Jan '95 the Duvall quake hit here and I was under a friend's '91 Honda Civic when the floor went sideways, shooting the axle stands out. I also had the jack under there and blocks under the wheels, which is what likely saved my life.
I heard a noise that sounded like a truck coming up the driveway while I was way under the car, looking for oil leaks (the car was lowered 3 inches and when it went for an oil change they claimed the drain pan was caved in rolling off the rack when it was the drain plug not tightened enough by the "mechanic" resulting in all the oil draining out on the way home. They were going to charge him $800 for a new oil pan so they asked me to take a look)
I was too far under to get out when I saw the car going over. It bounced off the blocks, shooting them out then it came down on my head. I tried to grab ahold of something to stop the car (back in the late '70s I trained to be an Olympic weight lifter) but nothing was there solid enough. I felt the crunch when it hit. The drain plug of the oil pan I had just tightened hit my head near the temple, punching a hole in the bone but it didn't break the skin and it caused a basal skull fracture from the occipital opening (eye socket) across the top of my skull, forcing my eye out of the socket.
I finally found something solid (I think it was the axles) and the adrenaline effect allowed me to bench press the car and throw it backwards, through the wood garage door as my friend came running because he heard my scream. I kicked the wall so hard that I crushed the sheetrock against the concrete behind it and left a permanent imprint of my boots.
Mr friend freaked when he saw me with my right eye hanging out and blood coming out of my left ear (I had a tear in the lining of the ear canal and later found out the anvil and stirrup were torn apart) I was going to drive myself to the hospital, but my friend's family kept me from doing that and called an ambulance.
The Dr in the emergency room cleaned my eye and popped it back in the hole and then they did a Cat scan to see how bad it was. They kept me in there overnight in the trauma ward. I overheard a couple nurses say "poor guy. He's not going to make it" but I'm not sure if it was me they were talking about. I stayed awake until the next day when the Dr came to check on me and I said "I'm still here!" so they took me to a regular room and I slept finally.
I didn't have any phone numbers on me for them to call (I was divorced and no cell phone yet) and the only person I could think of them to call was my then girlfriend/now wife of 18 years (we were married a few weeks later on Valentine's day) She informed my ex and kids plus my mom (who kept it from my dad because he'd had a heart attack recently)
I was up and about in 2 days (they kept offering me pain medication but wouldn't allow me aspirin) and I called my dad to tell him the news. When my mom put him on the phone, I said "Thanks!" and he replied "For what?" "For giving me such a hard head!" and I explained what happened and that I would be okay aside from double vision and only hearing from one ear (I later had microscopic surgery by Dr Noel in Vancouver, that restored 80% of my left side hearing the other Drs said was gone forever. He went through my eardrum and essentially crazy glued the bones together again. It comes and goes a bit with wind and cold which is annoying but better than none! Took a year for the double vision to go away. I had to drive my 40 foot bus 150 miles to Seattle with an eye patch!)
I survived. 95% of people in this situation don't. Play it safe. Not everyone can be in the 5% that make it.