The new Younami mine, page-24

Because when drafting pleadings you need to set out your primary position (i.e. the thing never happened) and then you need to set out your alternative position that in the event the court finds against us on the evidence that the thing happened (which we deny in our pleadings), we say that the these other facts result in them not being entitled to the relief sought, or any relief.

You need to remember that the statement of claim and the defence are merely what each side has set out as their respective positions and an outline of what they're intending to prove on the primary issue(s). With that also needs to set out what their position is and what they intend to prove in respect of alternative positions in the event their primary position fails. It all needs to be in the pleadings because if it hasn't been pleaded, in either the statement of claim or the defence, then it is not an issue that can be raised in the trial.

Perhaps thinks of the statement of claim and the defence as being the 'game plan' prepared by the coaches for two opposing football teams. They have their main game plan, but then have a plan B in the event that the opposing team gets a couple of sneaky goals away.

Does that make sense?