The little plastic tab that holds ethernet jacks in place can break off. For standard
RJ45 cables and jacks that's not a big deal. It's easy enough to cut off the old jack
and crimp-on a new one.
Plastic tab that came off an RJ45 ethernet jack
There are however some nice flat-band ethernet cables that are impossible to re-do at home.
The wires are too thin. I was therefore rather frustrated when the tab broke off my nice flat-band gigabit ethernet cable.