There was a plastic line there already and that line hadn't been used in atleast a year (previous tenants kept their fridge in the garage). I remember asking the plumber if we should replace that plastic line and he said no, I even told him it hadn't been used in over a year.
A week or so after he did this work I'm walking through my living room and my socks are getting wet. At first I couldn't figure out what was going on until I realized that line had split (as I expected it to) and was leaking, said leak having moved into the living room where it was making the wood floors damp.
To this day I don't understand why that plumber thought that would be ok when I, as a complete layman, understood what happens to plastic lines that go unused for that long (they dry and crack).
I have had issues with compression connectors at the ends (they don't like to be too loose or too tight), and I've seen plenty of failures of the really crappy washers that get used in "female compression" connectors.
There is no shortage whatsoever of licensed plumbers who will do incompetent work. Fortunately there is a decent collection of companies making excellent plumbing products that are quite robust.
Current personal favorite failure modes:
Use of inappropriate water-insoluble flux. This usually doesn’t cause a leak, at least not quickly. It is, however, disgusting (petroleum crud and not-very-good salts being released slowly over months to years in cold water pipes) and is a code violation.
Use of copper in boiler condensate pipes.
Use of essentially arbitrary mixes of pipe tape and pipe dope.
Overtightening of plastic threaded connections.
Incorrect combinations of tapered threaded fittings and gasketed straight threaded fittings.