There's another one of those "Hot Topics", Butt connectors or solder joints? I've chased quite a few broken solder joints. I think folks overheat the wire when melting in the solder, this hardens the metal and I've found the wires broken right at the solder joint. But the same deal can happen with a butt connector, if the wires moves the flexing can work harden the wire and it breaks right at the connector.

I always use a brand name heat shrink tubing to help act as a strain relief and keep the connection clean. Jegs had some butt connectors with the heat shrink already installed, I liked those and I still went over them with more heat shrink tubing.