Whilst a wiring diagram can look very simple, the practical reality is usually more complicated.  A select few of us practiced wiring a ring-main socket and a pendant light fitting with a ceiling rose and two-way switches.  We observed BS requirements for earthing, colour coding, etc.  We commented that it takes longer than you might think to get the wiring correct, neat and tidy, even working in ideal conditions on a table. let alone working on the ceiling at the top of a ladder!  Nevertheless, fortified with tea and biscuits we got it all working safely, right-first-time.