Requirements

If you're a programmer, it happens all the time.  You write a program, it works and then:

Program A has to do this, this, this and this.  And it does.

Then comes:

But if it's Tuesday, then Program A has to do that, that & that as well.
And on Wednesdays, don't do that or that but we need this.
Thursdays are special though - it's completely different on Thursdays.
And, well, Fridays...  I think we need another program for Fridays.

I was quite fed up by the end of today.