I was called out recently by a repeat client, who said her bathroom light had started flickering. When I climbed up into the loft to check the problem, I found this.
The wiring had been left sitting right on top of the light fitting. Over time, the heat from the light had burned through the insulation and melted the connector blocks, causing the connections to loosen. It was almost impossible for me to tell which was the Live wire and which was the Neutral; they were all burned black. I had to cut out and replace that entire section.
I've seen the same issue many times but this is definitely one of the worst examples. I'm sure you don't need to be an electrician to see how dangerous this is. Basically, it was a fire just waiting to start.
If the client hadn't noticed the light flickering, I shudder to think what might have happened.
If one of your lights is flickering, please don't ignore it. Get it checked; it could save your life.