Here are some examples of what could go wrong if you don't take things seriousely!
Burnd out plugs, switches, connectors, cables, burned down printers or even death!
Wire was not correctly inserted in WAGO-221.
Cheap all in one mains-connector that got overload
Bad contact in terminal
Burnt ICE plugs
badly crimped connector on a single-pole switch
Burned printers
I'll add more if you send me some.