i have been wrenching for years and have made MANY mistakes. Trying to do things while learning at the same time. I have screwed up backlash on gears, couple weeks ago i did a belt change on the bronco i didnt remember to lock tight the vacuum pump mounting bolt and it came loose and messed up my fan. That was a stupid mistake but at least it didnt turn into much.
I lost my uncle paul when i was 16. he was working on his baby, a 92 dodge D250 with the cummins. 2WD, he was converting it to 4WD with solid front axle. he had it up on jack stands, and one of them buckled. Police figured he was tugging or yanking on something and the vehicle weight shifted just enough to take out the jack...
Since then when ever i have tires off a vehicle and im under it i use 2X 6ton jack stands (even if its a cavalier). last time i was under the bronco i had my jack stands, and 2X u-pull-it style stands (2 rims welded together) under the front frame horns, and had the cherry picker/engine hoist, which ever you call it, set with light tension, and a chain wrapped around the front frame rails. Sure it takes forever to set up, but safety is the most important thing.
ALWAYS over do it, never under do it. No matter how simple. Changing your breaks? jackstand+jack even though you arent under the vehicle. it could shift, and its good night at that point. No one wants to lose a family member over something so simple and sheer lazyness to safety. Jack stands - 80 bucks? probably less. Your life and good health, is priceless.