Our house is of the age where there is no neutral wire at the light switch. I discovered that they had ran a 3 wire to the switch in our bedroom for both a light and a fan. I had installed a light/fan sometime back and in order to make it work I repurposed one of the wires as a neutral and then put a relay at the ceiling fixture. This all worked fine for control of both the light and the fan.
Problem was if my HE was down we couldn't control the fan. There was an outlet just below the switch so I got energetic and was able to route a neutral from that outlet up to the switch. All the neutral was for was to power the smart switch so no real problem.
Then got up in the ceiling, dissasembled the fan/light to take the relay out. Put it all back together and it wobbled. WHAT??? Then I realized I had forgotten to tighten the screws into the ceiling box. And of course no way to get to them without taking things all apart again. Only added another hour and a dozen or so cuss words to the job..