In short? Lady luck!
I've owned a gen Omega Seamaster Chrono 300M; yes the fabled 3D facial SM everybody wants. I have done everything with it; para-jumps, diving, shooting range, you name it and hand to hand stuff (I am a bouncer ????) and after 10 years IT FELL APART! I kid you not! It was serviced 4 times in 6 years... 3 times under warranty! As I was told, a "design hitch" in the first series clockwork.
When the bracelet started to fall apart, I sold it.
I own a hand wound Omega Seamaster Chronostop from 1968, inherited it from my dad. The apple did not fall far from the tree. The watch has seen mayor hardship. My dad bought it new when it came out. In the 50 years the watch was worn... It was serviced twice! I took it on a dive this summer in Croatia. Works flawlessly. Sow... Both gen; one auto, one hand and 34 years difference in age and a total difference in reliability and quality!
I have owned a multitude of diving watches; Seiko, Citizen and a rep Marina Militare from Parnis. Last one stopped working after three years, but three years of hardship and it ran 3 minutes short every 5 days. Still that watch saw some heavy duty. The repairs were not worth it. Even the sentimental value was not worth it. It only resolved the question if I wanted a Pam and not pay the price of a nice new car for a watch.
Hence my point. Lady luck. If you buy a "monday morning model" (Dutch slang for a total dud, made on monday morning in a foul mood and a hangover after a hard weekend) it's just bad luck.
The same watch, bought from the same TD will function without a hitch for your neighbor.