I would like to put forward a theory. The more time you deal
with a particular builder, the greater the probability is of
telling that builder to fuck off. I have recently experienced this
and to illustrate, I decided to draw a graph:

There are a number of noteable features of the graph:
(0) The starting probability is > 0. This represents the
latent desire we all share when dealing with a builder for the
first time. Do I trust this person? Should I just tell them to sod
off? Will they be reliable?
(1) This is the the point in the graph where the rate of change
of the probability of telling the builder to fuck off is at it's
greatest. You feel manic, constantly up and down, you're still
trying to maintain a polite and professional front but various
things the builder does is starting to annoy. You begin to
seriously doubt the decision to hire this workman in the first
place.
(2) The probability approaches 1. You reach a zen-like calm and
at that point you tell the builder to fuck off. He seems suprised.
You no longer care if they finish the work. Maybe you can do it
yourself (you can't) or maybe you can get someone else in to finish
off (you won't). This is the point at which the job either gets
finished or it remains unfinished for months until you get a
different builder in to do some other work so you can entice him to
finish the original job at the same time.
The process repeats ad infinitum.