Sad, but so true, Gav. A lot of the "trade" love to maintain the "mystique".
As with most things, it's a matter of experience. When you've spent a great deal of your life graunching screwheads, drilling into pipework etc, you learn.
I could tell you, just from looking at it, what the problem is, but maybe not from here though :o(
Either........ screw too big for rawlplug ..........
screw too long for rawlplug ......
If no plug, then ........... (into wood???) .......... drill a 3 or 4mm pilot hole first................
What are you screwing into?