What are outcome-changing circumstances mentioned in Augury and Divination?

This is one of those naval-gazing questions that may have actual mechanical bearing. Both Augury and Divination predict the outcome of future events:
In the case of Augury

“the results of a specific course of action that you plan to take within the next 30 minutes”

and in the case of Divination

“a specific goal, event, or activity to occur within 7 days”

Where I’m having trouble is deciphering the caveat found in both spells:

The spell doesn’t take into account any possible circumstances that might change the outcome, such as the casting of additional spells or the loss or gain of a companion.

A plain reading of this seems absurd to me, basically amounting to
“outcome X will happen unless circumstances are such that outcome X does not happen”
or
“outcome X will happen unless it doesn’t.”

For example, a prediction of “you will defeat the evil warlock” might have a possible outcome-altering circumstance of “his archdevil patron makes a surprise appearance and obliterates your entire party in an instant.”

I can see a more charitable reading: “Outcome X will happen unless the party introduces outcome-altering circumstances. And this helps particularly in the case of Augury: There is only so much a party can do to alter the course of the events up to 30 minutes from now. But with Divination’s seven days? How is a party ever to know what contingent facts must hold in order for the predicted outcome to occur? What are “additional spells” when, for some members of the party, spellcasting is done as a matter of course?