I gotta add a funny story to this thread.
Years ago my roommate at the time was dating this girl. She had a mid-80's Chevy Malibu type car. It had brake problems. She had already had one shadetree mechanic replace the front brake pads. Didn't help. Same mechanic then replaced one of the calipers. Still didn't help. Then she had a different shadetree mechanic replace both of the rear wheel cylinders. Still didn't help. Not the girl's fault as the diagnosis was made by the people that worked on her car.
My roommate asked me to look at the car. A fairly quick diagnosis revealed that the master cylinder was bad and it was only making the back brakes work , fronts had almost no use. So I told her it needed a master cylinder and the part was around $50 at the time. The look on her face was desperation and the thought of spending more money on a problem that didn't get fixed after several tries and the money spent. My roommate backed me up saying if that was the problem , I was probably right. The girl caved in and returned the next day with a new master cylinder. Fairly easy job , got it installed in about 20-30 minutes.
I then give her back her keys and tell her to wear her seatbelt until she got used to how the car was going to stop. In one ear and out the other.......
She came back a couple days later to visit my roommate. Then I got the story.....lol
She had left with the car after I fixed it with another girl. The first real stop they made the driver was so used to pushing down super hard on the brake pedal they completely locked up the brakes. The driver slammed into the steering wheel and the passenger hit the dashboard and faceplanted the windshield. Obviously not wearing their seatbelts. Luckily nobody got hurt too bad. The girl that owned the car thanked me for fixing her brakes correctly unlike the people before that failed.
Moral of the story - Wear your seatbelts.