It is the most important thing in the world.
Especially when we are working on our cars.
I happen to have an eye opening experience just this week. I have a jack fail while lifting my car. It did some damage to the car but remember those are replaceable we are not. This is one of the most dangerous accidents that can happen while working on cars. I would like to take a moment and bring some good practices to your attention.
First and foremost make sure you know what you are doing and how to operate your jack. If you do not know how you should lift any particular vehicle find someone who does. Next always, always use jack stands. Also chock the wheels when necessary, that is any time only the front or back is in the air. Once the stands are in place slowly lower your jack until the car rest securely on the jack stands. Once it is down on the stands, shake the vehicle, not to hard but just to make sure its secure. I will typically leave the jack tight on the car (not lifting it off of the jack) just as an extra safety net.
Remember there are plenty of other things that are dangerous but never risk a car falling on you or anyone else to save a couple minutes in preparing a car to be worked on.
This is the gruesome truth that lifting a car is dangerous. I appreciate that I am still here today with no injuries, but that may not always be the case.